Their single 5 Colours In Her Hair, which was released on 29 March, is being played everywhere, they've toured with Busted and are even best mates with Charlie, Matt and James.
And if you missed it, you can catch it on the video below or just read the boys' answers in a transcript of the webchat.
Do you find it weird when you see yourself on television or you hear your song on the radio?
Naomi, 15, Walsall
When did you first meet each other and how did the band get together?
McFly: How did we first meet each other? Well we all met each other - Tom met Danny first through an audition that Tom was helping out for and they basically met because Danny auditioned and Tom really liked his voice and his playing and stuff. So they went and chatted to each other and Danny started going down to London and writing with Tom and stuff and basically they became friends like that. And then they got all these McFly songs and got the record deal and needed a drummer and bass player, so they auditioned for me and Dougie.
Now what about the name, is it from Back to the Future, because I'm always going McFly, McFly to people and that's before I even heard about you guys?
McFly: No it definitely is Back to the Future, it's from the film. Well basically Danny didn't really like the name at first, because I came up with the name and everyone liked it apart from Danny, and so it's quite important that Danny liked the name. And I said sit down and watch the film with me and we watched the film and the bit where Biff crashed into the manure truck, it says Danny's name on the side of the manure truck.
Mattie, 14, Blackpool
What or who is your song 5 Colours in Her Hair about?
McFly: It's about a girl called Sooz, who's from a TV show called As If and me and Danny basically we were in a hotel and we were there for about a month and all we watched on TV was this programme. And we just thought she was really hot because she's got like loads of dreadlocks and colours in her hair and piercings and stuff and we ended just writing a song about her.
Nicole, 12, Falkirk
How will you celebrate if you go to number one in the charts as I'm sure you will?
McFly: Shall we do an impression of what we're going to do? If we get anywhere in the top 10 we'll just probably have a party or something.
We don't know, we've never been number one. We'll celebrate if we're in the top 10.
Lauren, 15, Telford
Hey guys! Does it scare you that you've become so popular so quickly and by the way I think you're all gorgeous and I love you loads?
McFly: Thanks Lauren. Yeah very, very scary. It's scary because we don't know why. It's really scary, it kind of happened very - not slowly but it was obviously like you said it was so fast but it started like in December and gradually since then it's just got more crazy and it's just really cool and thanks everyone for supporting us.
Did you go out and buy your own single?
McFly: Well you know why not? Yeah, we went to Woolworths and filmed it as well.
How many singles did you buy each?
McFly: We bought two each CD1 and CD2 - you have to support yourself don't you.
Laura, 13, Stockton
What are the best and worst parts of being on tour?
McFly: The best part of being on tour is being able to play every night and staying in hotels and not having to clean up after yourself. The worst part is you have nowhere to change your underwear and stuff, so you just get a big fat pile of it.
Lana, 12, Louisville, USA
What makes you a unique band and not just a carbon copy of other boy bands?
McFly: That's a good question. I guess it's because we're not like any other pop bands that like can't play guitar and stuff, we're like an actual pop band - we've got a drummer and a bass player and things like that.
We've been playing since we were like five years old as well.
Usually when you think of a boy band you think of sort of just people that just sing and perform and we play the music and sing it. People can call us a boy band if they want, it's just that people sort of have a set image - if they haven't seen us before and they just read that we're a boy band they might just think that we don't play our instruments or things like that.
When McFly started out we literally were literally were four guys that were just going into rehearsal studios and just jamming and just rehearsing and stuff and to us that was a kind of bandy thing, so we didn't see ourselves as a boy band.
Becky, 14, Oxfordshire
If you could collaborate with any band or artist, dead or alive, who would you choose?
McFly: We'll do one each.
Harry: I'd do a drum duo with John Bonham and he's the Led Zeppelin drummer.
Danny: Have you ever heard of Bruce Springsteen?
Dougie: I'd have to collaborate with Aqua.
Tom: I'd love to do a duet with Paul McCartney.
Shamin, 14, Leytonstone, London
If you were to be reincarnated as an animal what animal would you be?
McFly: Danny would be a rat.
Harry: I'd be a donkey, I kick.
Tom: I'd be a fish.
Dougie: I'd be some form of reptile I guess.
Jo, 11, Poole
How much did Busted help you out?
McFly: I think they helped us out a lot, especially James because James has been involved with us right from the start. He's got a bedroom at our place that he uses whenever he stays with us and when he writes with us. But James has been involved right since the beginning and even before I met Danny me and James sort of wrote a couple of songs which are sort of very '60s influenced and that's where we sort of said oh this is really cool and it didn't sound anything like Busted, so we sort of said this should be like Tom's sort of thing and that's where it all came from. So James has been involved right from the beginning and of course Matt and Charlie have really supported us.
In interviews and stuff they've been really sort of - they've always said, right back in sort of October they've been like oh yeah there's McFly coming out soon, look out for them and stuff.
And then letting us go and support one of their tours. Thank you Busted.
Clare, 13, Watford
When is your album going to be out, I'm desperate to hear more of your tunes?
McFly: The album's going to be out in July - the first week in July - so it's not that long. But we're going to have a second single first, which will have B sides on, so there'll be more songs there and then the album. So be patient.
Gemma, 15, London
Do you hate it when people say you're just a rip off of Busted?
McFly: We don't get annoyed when people say that we're a rip of Busted because James has written a lot of our stuff as well. I mean you can understand it, as in the sense that we dress the same and stuff.
Elizabeth, 14, Horsham
If you were to go on your own tour - which I'm sure you will at some stage very soon - would you ask Busted to be your support act?
McFly: That would be cheeky, no.
Who would you ask then?
McFly: We want a girl band - Clea.
Laura, 14, Essex
I know you're really good friends with Busted so if you could have one of them in the band who would it be?
McFly: We should have Charlie so we can have two drummers.
No then you'd have two posh people - that would be mayhem.
I think James would fit in the most.
I think James - I think we owe it to James because he co-wrote a lot of our songs.
Matt would be fun to have actually.
Yeah Matt would be cool as well.
I choose Charlie.
Right, I'll choose James and you can pick Matt and then it's fair.
Zakia and Hamid, 13 and 11, Birmingham
Tom how did you feel when Charlie took the final place in Busted instead of you?
Tom: I was angry. No I was really upset because I'd heard a couple of the Busted songs at the audition and stuff and you know I really liked it but I'd already - I'd met James and everyone and I knew that we really got on and it was sort of when I didn't get in I'd already sort of started showing them my songs and the management had shown an interest in me as well, so it wasn't all disappointment. But I was quite - I was really disappointed.
Chelsey, 15, Tewkesbury
Did you ever argue with Busted on tour?
McFly: No. No we hardly have any arguments between ourselves, let alone Busted. There's no time to argue. Apart from when Matt stole Danny's guitar.
What do you think about the row between Busted and Girls Aloud?
McFly: No, I think that was just something small that they said and they didn't really mean. I think everyone sort of picked up on it and it got out of hand. But we don't really know much about that. We haven't met Girls Aloud yet.
Sara, 14, Kenilworth
Can you dish some dirt on any of the Busted boys like do any of them have bad habits?
McFly: I went out with James one night I was talking to him in the car and I asked him a question and it was some very, very easy question to answer - it was a one word answer - and half an hour later he answers it, he just blew me out.
When you talk to James he doesn't listen to you, he just looks the other way. He's in his own world.
Rachel, Tyne and Wear
What was your favourite arena and your best moment on the tour with Busted?
McFly: Wembley was my favourite.
Manchester was my favourite just because I've seen all my idols play there and that's where I'm from.
I very much enjoyed Sheffield. It's a good arena - good acoustics. It was really cool backstage at Sheffield as well.
Elizabeth, 14, Horsham, West Sussex
Can you dish any dirt on Busted?
McFly: I think that was it about James wasn't it before. It's not our place to tell Busted's secrets.
Naomi, 15, Warwick
Tom if you were a girl for a day what would you do?
Tom: I'd go probably shopping because girls' clothes are so much better than guys' clothes, they can get away with so much more.
Lauren, 14, Birmingham
Danny, if you weren't in the music business what job do you think you'd be doing?
Danny: Well for work experience I did joinery, which is fitting bedrooms and kitchens and stuff. I quite like joinery.
Tom you used to be actor didn't you?
Tom: Yeah I went to theatre school. I did a Curry's advert and I had the worst haircut I've ever had in my life. I had to be this choir boy as well, it was horrible and I had like really long blonde curtains and I felt such an idiot and I think they played it again last Christmas as well. It was very embarrassing.
Tom is it true you collect teddies?
Tom: Well no I don't collect them, it's just that I had a few and then like some fans started getting me them and now everywhere I go fans give me teddies. They're just all on my bedroom floor.
Danny, if you could change anything in the world today what would it be and why?
Danny: Anything in the world - I would change wars and have world peace.
Cara, Berwick Upon Tweed
Is it true that you boys don't wash your jeans?
McFly: Yeah, we don't wash our jeans.
Abigail, 15, Dudley
Your fans ask you lots of questions but what would you like to ask your fans back?
McFly: Why do you like us? What is it about us that you like because we want to know? It's very cool that you like us. We like our songs.
Laura, 14, Hatfield
If another band started slagging you off what would you do?
McFly: I think it's wrong to slag off other bands, even bands that I don't listen to I'm sure there's hundreds and hundreds and thousands of people that like them even if I don't. Each band believes in what they're doing and so obviously that's all that matters so I think each person doing what they're doing we always usually just wish them the best of luck in what they're doing.
Becky-Lou, 15, Watford
What has been your fav song to perform on tour during the last month?
McFly: Saturday Night or That Girl.
Room on the Third Floor.
Kerry, 15, Scunthorpe
I do a bit of song writing myself but I don't think I'm very good at it. Have you got any advice for me?
McFly: Stick at it and don't give up. I was really, really bad at first, when I first started writing songs, I kept going back to the management and showing them songs and they'd tell me to go away because they were really rubbish and they told me just to like go away and change certain bits and come back. And also take criticism well, like Tom's biggest - our manager's always saying the best thing about Tom is that when he gets criticised he always takes it as a good thing to go away and try and make it better.
I wrote whatever came into my head first and then made it better.
Olivia, 12, Stourbridge
What do you do when you get really nervous?
McFly: I think we all get nervous about the same things, it's only just before we go on stage that we get really nervous. So if we know that we're all nervous together then it's not so bad. And as soon as the curtain opens on stage, as well, we've forgotten about the nerves anyway.
We just look at each other and say let's go for it. Nerves are a good thing anyway.
Laura, 14, Blackburn
Do you do anything before you go on stage for good luck?
McFly: On the Busted tour Harry always had to go on stage first.
I don't know why I really like just want to get on stage and sit on my drums and just get ready.
And Dougie's always second and then Danny and then me last, which is bad because I have to walk past them all then to get on the other side of the stage.
As from this Sunday you guys are probably going to become household names, if you're not already, because we reckon you're going to go to number one. How are you going to cope with the fame? Dougie I'm going to ask you that first.
Dougie: I don't really think it will happen like that, I think it'll happen over time.
McFly: We'll just stay normal. Like we say in our song - How does she cope with her new found fame? Well how?
The thing is it doesn't actually feel like it to us anyway, you know how you see like other people get famous and you know other people's names, it doesn't actually feel like anyone else knows who we are or anything. So obviously we're going to stay normal because to us even though like people recognise us and stuff like every now and then and our fans that really love us and stuff but like to us it doesn't feel like we're famous.
Me and Tom wrote a song about keeping our feet on the ground.
Megan, 16, Coventry
Are you nervous about listening to the charts on Sunday?
McFly: Yes. We're all going to sit down with all our families and stuff.
Hannah, 11, Warrington
How have your mates reacted since you've been famous?
McFly: I've got one best mate that always comes down and the others are just college mates, just one best mate and he's awesome.
A lot of the time you see your friends because you want to get away from it all but you end up just talking to them about it. You don't mean to but you kind of just want to tell your friends because you want to let them know what you're doing and so I just blabber on about it.
I'll tell you a little secret - on my 18th my friend actually cried on me.
I don't have any friends apart from the other guys in Busted.
Jenny, 15, Wirral
What's the craziest thing a fan's ever done?
McFly: One of them screamed at Harry in Sheffield.
I went to go to the dressing room to say good luck to Ant [phon.] because he was performing Where is the Love with Busted and I was innocently just like walking along and literally she started screaming in my face. But I thought I'd done something wrong - she was really close.
Things like that really surprise us because you don't expect them to happen to you.
Have you gone back home and been recognised yet?
McFly: Since it's all taken off over the past month we haven't really been home. We're going back next weekend so we'll wait and see.
Hannah, 15, Coventry
What's the best thing about being famous?
McFly: We're not famous yet.
What's pretty cool is when you do TV and things like that you get given free stuff, we get given so many sweets.
We get given wind up phone chargers - if you're ever lost and you didn't have a phone charger we've just got these wind up ones, so they're cool.
Another thing is when like we did a signing the other day and there was like lots of people just to see us and that's a really cool feeling.
And the other thing is we get to meet a load of famous people.
Georgie, 12, Farringdon
What's the weirdest gift a fan has given you?
McFly: There's been some rude ones which we won't say.
I got given a chocolate lolly the other day, it was on a stick - it was at the signing - so I just put it behind me like that but I forgot it was there and I sat on it and I sweat loads anyway and I got really hot and bothered and when I stood up at the end when the signing was over it was all melted all over my shorts.
Esher, 12, Potters Bar
What's your next single going to be called?
McFly: Well we're still sort of deciding what our second single's going to be but we think it's going to be a song called Obviously. But it could change.
Kirsty, 15, Stanley
Do you find it weird when you see yourself on television or you hear your song on the radio?
McFly: Yeah we heard our song on the radio the other night for the first time, didn't we.
The first time we saw ourselves on CDK I watched it and I just totally forgot that other people were watching. It was like watching a video tape of ourselves and even now when you watch it you think oh I looked a bit sad there but no one else is going to know.