I don't buy the whole "you have to leave behind everything from your childhood as you grow up" mindset. Some things, yeah, you don't need to keep with you forever, but that isn't everything. If you still enjoy something, or get positive feelings out of a show from your childhood, I say there is absolutely no reason why you should give up watching it. I do, however, believe that you should add new stuff to your life as you grow up. But that isn't replacing the old stuff, that is merely broadening your horizons.
Though I do think some things are better left unsaid to certain people, such as liking a kids show excessively. Close friends, family, sure, tell them, but with acquaintences, it can look weird and throw them off. People close to you see it as just one aspect of you, but people who don't know you well could be quite put off. It's none of their business, anyway, as far as I'm concerned, especially if they wouldn't understand.