Pit bulls are NOT the only breed that sometimes attacks for no apparent reason. Dogs are living things, and thus are somewhat unpredictable, no matter how well trained.
Because of that, I would NEVER let a child play with a dog that wasn’t a lot smaller than the child, just as I would never let my child play with a big severely retarded guy wielding a knife. The retarded guy might be the most gentle person in the world, and would never intentionally harm the child, but is not smart enough to realize that what they consider play might be dangerous to the kid, and he’s holding that knife… It would be just asking for something bad to happen. Likewise, dogs are not as smart as us. They always have dangerous weapons on them (their teeth and claws). Dogs sometimes involve biting in their play, and the dog equivelant to a playful punch on the shoulder between humans can seriously injure a human. A dog also tends to react to negative stimulus without considering the cause of it like we do. Some dogs have sensitive spots they don’t like to touch - my uncle had a dog that was great with kids, as long as they were warned ahead of time not to pet or touch him under his chin - he did not like that and would snap. Kids also do things when playing with dogs that would hurt any dog, like pulling or blowing in their ears, spreading their toes too far apart, etc.
Humans also have a different surrender reflex than dogs. An adult dog will often grab a pup with it’s jaws and give it a little squeeze when it’s misbehaving. The pup will go limp and roll over if it can…if it doesn’t, a little more pressure is applied. A human given a correctional bite probably won’t respond properly, and the dog’s instinctual response can be harmful.
My take - all dogs are potentially aggressive. You can never be 100% certain that it’s not going to bite someone. You are responsible for the actions of your pet, therefore it is in your best interest to keep it under your control, especially if it is big enough to do serious damage (though even the smallest dog can hurt someone enough to need stitches). I think as a potentially dangerous thing that requires caution and understanding to interact with safely, young children should be kept away from dogs. I think dogs that show a pattern of overly-aggressive behavior should be put down. As to single instances, I don’t really think it’s fair to the dog to put them down for one bite as even a good dog can have a bad day, but it might be a good idea anyway.