Indeed, not only Americans dress like children. If you will travel in the Europe you will see many countries where people the same dress in bright colors and clothes with funny prints as a nursery. I found it nice and I don't see the problem in this. Such way people express their individuality. Maybe, that had no such clothes in childhood, so, they are now compensating it. The main thing is that people were educated and mannerly. On the other side now many children's clothes are of such style as for an adult. Really, made like for small ladies and gentlemen, like these
https://ooyoo.co.uk/ . So, that's just the question of everyone choose. Don't take care of this.