My prayers are with the child and family...
Durbins three dogs, bit another of their dogs and Melissa Durbin before attacking the boy.
You can't have a dog with a history of biting people, especially an owner, around a baby.
Here is the reality of owning a Pitbull... If you acquire from a reputable breeder, you are going to get a well bred dog who is energetic, loyal to the family, adores children, does not take to aggression against humans but
is animal aggressive. These are the things pit bulls were traditionally bred for. You are going to have to spend quite a bit of time with it to make sure it develops properly and has outlets for its liveliness.
If you do not, you cannot be sure how the line was bred. There could be rampant inbreeding leading to genetic defects, even brain damage(which can lead to aggression out of the blue). The dogs could have been bred for brutality, which means you will be fighting against breeding to have it be peaceable around humans. Of course it could be the nicest dog in the world, but you just don't know what you'll get.
If you want to get a pit bull, buy from a reputable breeder, or, even better, the local animal control/pound/shelter/etc. where they do behavioral tests to determine whether the dog is ready to interact with humans positively.