I've always wondered this also, why children are always abused by adopted parents or foster parents... I've always wondered if the type of person who is predisposed to want to adopt a kid will usually also have a predisposition to being violent towards children as well...

Because I know that I could never be violent or abusive to a child ever! But at the same time I wouldn't want to adopt or foster one... So I don't know... I think more studies needs to be done because a lot of kids suffer that way..