I like the gameplay for the games but I don't like how all the characters look like kids wearing skimpy clothing.

Probably not to your liking, no. Looking like kids (and, in fact, basically being kids) is standard faire for JRPGs, Anime, Manga, etc. If you haven't saved the world at least twice by the age of 15, you're a failure. You don't have much choice over who your main characters are (some non-main characters have robes & such that are probably more to your liking) or what they wear (you can give them different outfits, but they are mostly about similarly covering except the swimwear). I'm not sure I agree that the 4 main characters are wearing too-skimpy clothing, although I guess in HDD form you might think that. You will be spending most of the games in non-HDD form.

edit: you might be happier with the Trails series. Similar mechanics, but then again, there was one character everyone complained about in 2. Maybe it's best to just steer clear of Japanese games.

Well actually kids there are candidates (teens from 12 to 14) and man characters are late teens\young adult (somewhere 16-18)




Spoiler:
(you can see adult neptunia in vii, in black uniform and with bigger breasts)