Liking cartoons, Pokémon, video games, acting silly and say retarded stuff to try making me or other people smile, is a good kind of childish.
Becoming a bitch for no reason, ignoring me if I don't do what she wants, when she wants, giving me the cold shoulder instead of talking problems out; that's a bad kind of childish that I wouldn't really tolerate.
As for general turn offs:
-Flirts too much with guys everywhere
-Always expects me to do everything, without even giving me suggestions
-No sense of humor
-Judges people for insignificant things, such as clothing
-Doesn't speak her mind, keeps things in from me when she would have told other people
-Inconsiderate - doesn't think about my reaction before doing something that will affect me