Pitbulls are used as assistance dogs in the USA.
I have never seen a dog attack report where I didn't feel or suspect that the humans were at fault, not once.
Children should not be left alone with dogs, at all, ever, because children can't always control how they behave, nor are they always aware how they should behave and they could do something that makes the dog feel it has to bite. Bad situation for the child and dog.
Dog owners should have to pass a test prior to be able to own a dog. Too many parents allow their children to clamber all over dogs, take things from them etc and are then suprised whent he child is bitten as they think the dog was 'good natured' and 'used to children' and 'a wonderful family pet', when in fact the dog had simply been putting up with what amounts to abuse for years until it couldn't any longer. 
I've got four dogs here, three pedigree Golden Retrievers and a staff cross. I'd trust any of them with my DC, I can't imagine any situation in which they would bite, but I just wouldn't risk it because I am both a responsible parent and dog owner.