Because the media and most online statistics label anything they can't identify, most crosses and anything that looks like a 'fighting dog' a pit bull...
The reason these dogs attack can simply be a 'correction' by the dog, because it sees itself as alpha. But because humans and human children are so much squishier than another of the canine race, it doesn't always end well. If you look at those statistics, most are either unsupervised children, or chained dogs, meaning the one who was killed would have had to have been close enough to be bitten.
Attacks over 6 years '94-'99
28 rotties- 9 guard dogs, 8 unsupervised kids, 5 loose, 5 chained, 1 family dog
6 pit bulls- 1 mum threw baby to dogs, 2 loose, 1 owner away, 1 family dog, 1 newly aquired
8 pit bull types- 3 unsupervised, 2 loose, 1 feeding, 1 family dog, 1 aggressive because of owner, 1 protecting his dog
16 mixed breeds- 3 loose, 8 family dogs, 1 newly aquired, 2 unsupervised, 2 chained
Over 2 years '01-'02
9 rotties- 2 infant death, 2 got loose, 2 unsupervised, 2 family dogs, 1 chained
8 pit bulls- 5 chained, 1 guard, 1 loose, 1 owner possibly had seizure
4 mixed breeds- 2 chained, 1 loose, 1 infant death
Looks to me like humans are more to blame than the dogs
Over all:
15 unsupervised
15 chained (which means they had to be close enough to get bitten)
14 loose
13 family dogs
9 guards
8 misc
3 infant deaths