So when does the change happen that causes some to mistreat children the way they do.

goo, goo. You can't help it can u??

Same thing with kittens meowing and puppies howling and whimpering. Their designed to get the same reaction from their parents and because humans are empathic (not telepathic, not the same thing), we react in a similar manner.

good question, indeed! if we know the answer we can do something to change that behavior, i guess.