Is there nudity in any of the Mobile Suit Gundam series? I heard somewhere that there is some nudity in some of the Mobile Suit Gundam series, is this true?  And if so, which ones have it and how sexual is it?

I want to watch the shows with my little brother and I just want to make sure there's nothing like that in it before we start it.
For the portion you're concerned with
IMDB states the following-

Some characters (including children) do appear fully naked in bath scenes. Breasts are visible on female characters, and penises are visible on two child characters in one bath scene. There is a scene where one male child character rubs the chest of a female child character, though this is more comedic than sensual.
There is implied to be a romantic interest between many characters on the show, but nothing sexual is even shown (or for that matter, hardly even implied.)

List of Bathing Scenes-
http://animebathscenewiki.com/index.php?title=Mobile_Suit_Gundam
For additional info you may refer to this link-
https://m.imdb.com/title/tt0159172/parentalguide?ref_=m_ttpg