I do not think it is wrong for childless adults to watch children's movies. Perhaps a bit out of the ordinary, but certainly not wrong. When my children were much younger, I watched movies with them, but it was out of a sense of spending quality family time together, not because I was particularly entertained by the movies. Different strokes for different folks. However, there are some settings in which it may be odd or unusual. If there is some type of showing or premiere event that has been advertised and geared primarily toward the entertainment of children, I don't think it would be a good idea for a childless adult to attend. That could come across as a bit creepy, especially in such a day and age in which people are hyper-vigilant when it comes to child predators. While it wouldn't necessarily be "wrong" for an adult to attend for their own entertainment, it would probably just be wise to avoid those settings and watch the movie at home.