Have adults who speak in very childish voices had something traumatic happen to them in their childhood ?

Um…...... yeah? It’s possible. It could totally be a way in which more aggravated dissociative states present themselves (as could all voices – like, gruff and deep and male on a teeny, high-pitched female). But, there’s also tons of other reasons among them for that, the biggest being that that’s just how some people talk, especially females. Or, simply being more socially conscious – I’m more likely to talk in a “child’s” voice, as it were, when I’m in a classroom setting and have to watch what I say than when I’m drunk in a bar and letting F bombs fly, or tired and kinda crabby. So, one of many, many reasons. And I would think if it was coming from an attempt to remain a mental child, the person would be more likely to use children’s various vernacular (eg baby talk, LOLspeak) than a soft voice, though they could easily combine the two.

I don’t personally know anyone who speaks that way.
I do know quite a few people who went through sever childhood trauma, and most of them have quite gruff voices. It’s funny I hadn’t consdiered it before.

According to mental health professionals, like Henry Cloud, if a person has a traumatic experience in childhood, it can stunt their emotional maturity and development. However, I never thought about it affecting a person’s vocal patterns. It’s possible, I suppose. Alternately, it could be that the person receives more positive attention from others when they speak that way, and so (either consciously or unconsciously) they maintain that voice.

It is a cultural convention to seem younger and thus more desirable. So no.

I think it’s more of a habit than caused by a trauma. My mom frequently said to me as I was growing up, “Lower your voice.” No piping childish voices for her. It worked. I can sing tenor (but don’t).

I think it can also be a cultural effect. My company employed a fantastic Japanese woman as an interpreter. When she spoke in Japanese she used a high pitched voice which was more culturally acceptable to Japanese men. When she spoke English, she used lower pitch. It was incredible to watch -a bit like watching Seth McFarlane when he instantly switches from character to character in the clip at ~1:50.