This is another example of MN existing in a parallel universe. I don't know anyone who owns a pit bull/staffy type dog or would be entirely comfortable with their kids being around them, even though there are certainly quite a lot of them about these days.
I am comfortable with certain dogs being around DS. I am uncomfortable about certain other dogs being around DS. The ones I am comfortable with are the dogs that I know have been socialised and trained. The dogs I am uncomfortable around are the ones that have not been socialised and trained. This is irrespective of breed, age or sex. A well trained and socialised dog should be able to be around children. A poorly trained and unsocialised dog is a risk being around children. And that has nothing to do with breed.
I have a friend with staffies. Her young child has grown up with them, and the child competes with the dog in competitions. I've also run with this dog in a teams event and he's an entire (not desexed) male, I have never seen him even glance sideways at another dog, and I am quite comfortable running my own dogs with him and I've seen him with the child running him and he's amazing with her. I have no hesitation allowing my son to interact with this dog.
I know this dog, I know what he is like, and I will interact with him, and allow my son to do so. That doesn't mean that I allow my son to run up to a strange dog in the street. I'm teaching my son to ignore dogs in the street, or ask for permission to pat them. He is 3 1/2, but he knows already not to touch a dog unless the owner says it is alright, and this is a child that is surrounded by dogs.
No dog owner will say that their dog is aggresive or unfriendly. Their's is always the most sweet dog in the world. Then the mauling happens "out of nowhere".
Actually, the sensible dog owners will know their dog. My male is not good with other males if they come in to my yard due to an attack in his youth, so I don't let him run him with other males at home (he's fine when he's at shows or events when it's not in his backyard). He's not looking to fight, but he gets very defensive when any of the girls are with us. So I don't put him in the situation where he could feel he needs to defend himself against another dog. But I will allow this dog to play with my son because he is fantastic with him and supervised play is a great time for both of them.
There is a big difference between human aggression and dog aggression. Dogs that are not good around other dogs aren't unusual, and it is actually fairly easily managed. Dogs that are human aggressive are a different issue and need specialised behaviouralist intervention. It is incredibly rare to find a dog that is dog AND human aggressive, and that would normally be a dog who has severe behavioural issues, and should definitely not be out in public until those issues have been addressed.
Most of the 'out of nowhere' maulings are actually due to the behaviour of the child or adult. I cringe when I see pictures or videos of a child climbing over a dog, taking food out of its mouth, shoving it, squashing it, pushing it. Every dog owner should read this article: www.suzanneclothier.com/the-articles/he-just-wants-say-hi as it is the best article about canine behaviour that I have ever read. Dogs generally 'react' rather than 'act'. A dog that bites has usually already given many signals that they are uncomfortable in the situation they are in, and the bite is the final 'telling off'. Know your dog, know their behaviour, know their limits, and the chances of biting are far reduced. Likewise, teach your children how to behave around animals, and don't put your pet in the position of having to defend themselves, and you won't have problems.