I once saw someone (an autistic someone) who had some trouble with word-finding, and would gesticulate a bit at those moments. For a second, I could see part of where a "childlike" impression could come from. It looked kind of like how kids look when they're just starting to learn how to express themselves verbally. (It's not something that would make me think of or treat someone "like a child," though.) I suspect there's a lot of other things that lead to that impression, though.
Sometimes, I feel like a kid in an adult body, but at other times like an adult in a kid's body, sort of -- due to other people's projections. There is an evil little impulse in people that I (nowadays) can spot, but that they can't tell that I can see. It's the "I can mess with the person and they won't be able to tell, so I'm going to do that" kind of thing. ...And a lot of other experiences in life that I've had, and that inform me, but that apparently don't "show."
Also, I've found at times that it can cause people to let down their guard and reveal themselves, making it easier to see who they really are.