I have come across purely mechanical reasons that explain why children have piping/high pitched voices - length of trachea etc. However, I find myself wondering whether there isn't a deeper evolutionary reason why the mechanics evolved that way. Is there a Kinderschema type explanation for this? I have attempted to find information on the subject and turned up nothing - perhaps because I am simply not searching for the right thing. Perhaps someone here can help.
While I am not aware of any such theories, and personally would find it hard to follow the reasoning of any such evolutionary argument.
I would however suggest it pretty easy to argue the evolutionary benefit that we adult care givers consider 'cute' the vocal characteristics our offspring are capable of producing.
So any evolution in my view is likely to be in the ears and minds of the parent instead of the vocal tract of the infant.
I am unaware of an explanation, this is totally anecdotal, but from my experience the pitch of my children voices and their screams for affection or attention often seem to short circuit my thought and make it impossible to do anything but help them. Where as I don't experience the same reaction to a lower pitched call. Perhaps I am on high alert to their needs but it seems more to it than that. I have twins one is lower pitched than the other and I am able to delay response a little better to the lower pitch. I have no idea the relationship between my mental makeup or particulars about my personality and how I respond to these sounds but you may find this useful in searching out more information.