Is Ninja Hattori a cartoon or anime? I've been watching this thing since I was 8, now I am curious to know what I've been watching all these years. I am not sure what makes an anime and a cartoon different, but I think anime has more violence content than cartoons.

In many of Ninja Hattori's episode, use of weapons, like sword and shuriken was shown. And in most of the episode you can see Hattori and Amada fighting, which is not suitable for a cartoon. Those fights can be compared to the fights in DBZ or other action manga and animes. 

So what do you think, is it a cartoon for children or a action genre anime/manga?
It's Anime because it's made in Japan, and (generally) made for Japanese people.

Cartoons are animations in a broader sense, and as such, Anime is a form of Cartoon.
Made in Japan.

http://myanimelist.net/anime/4936/Ninja_Hattori-kun

It lies in the rating of the show and its targeted audience to determine what can be shown to viewers, low violence doesn't make something a Cartoon if that's what you mean.