The pit bull groups of dogs, as breeds, are not the nanny-dogs that people claim they were. They are mastiffs; they were intended to guard, and were used for hunting and war. You can train the shit out of them, and they can still revert to breed characteristics.
A study in the US concluded that greater than 60% of all fatal dog attacks in the US were from pit bulls or Rottweilers, but those two groups don’t make up nearly 60% of all dogs in the US. These simply aren’t breeds that should be left alone with children.