Until they're not. Most dogs are good until they're not. The young woman who sadly died today may well have said yesterday her dog was good.
A large dog ( and I'm a previous large dog owner) who let's loose can be very hard to control if attacked by/or attacking, another dog.
I once had to try and separate a small medium sized dog from a very small dog, it had latched its jaws around its throat. The owner of the attacking dog was nowhere to be seen. The owner of the small dog was utterly traumatised, as was the small dog, it did survive but was never the same again. There were 10 people around me and despite various tactics couldn't get the dogs separated, I can't even remember how they separated in the end. I now know what to try but then I had no idea, hosed water up the dogs face, pulled its hind legs, it was nightmarish and that was a relatively small dog. I was very aware it could have turned its attention onto me.
My own dog is drawn to small children he is a smallish terrier and has a high prey drive, I don't think he would bite as in anger but children are loud, excitable and move quickly, all his triggers , so my dog is on leash if children are around. Im coastal so i can see well ahead if anyone is coming in my direction. Even him jumping around them would be too much. I have a harness with a handle on the back to catch him if needs be too. I wouldn't have an xl bully anywhere near me or my dog, never mind a child.
As hideous as it would be to put them to sleep these dogs should not be among the general public ever.