However, what the people who say that fail to realize is the reason those things can still be enjoyed is that they are not forced. For example, I love Disney animation. However, I do not enjoy reptitiveness. Children tend to watch things on repeat over and over. If I had to watch the same show, even if it was a favorite, thirty times in one day, I'd quickly grow tired of it and not want to hear another thing about it.
There's also a stereotype that if you like things aimed at children, but do not have any yourself, you haven't matured yet. It's utter nonsense. First off, every single thing aimed at children was created by adults. In addition to that, someone's preferences for what kind of entertainment they prefer has little bearing on their level of maturity. Personally, I mainly stick to media with ratings under PG-13/TV-14 because the more adult themes (swearing, sex, etc) don't interest me. Anything I watch over that rating is comedy.
Of course, interests do change over time and it's not wrong to have outgrown child-like entertainment for things geared more toward adults. But the idea you can't do something meant for children unless you have one of your own is silly. Eighteen is not a magical age where someone's interests morph the second the clock strikes midnight on that birthday. Sometimes, adulthood makes those things more fun than they were during childhood because you can choose them for yourself instead of being told what's appropriate and what's not.