There is a lot of bunkum talked about with Staffordshire bull terriers. You often get one camp calling them "nanny dogs" and the opposition claiming they have lock jaw. Neither is true.
Staffs can show aggression to other dogs, but often they are not the instigators. One of my own dogs has hidden behind me on several occasions to avoid a larger more aggressive dog.
They were originally bred as fighting dogs. When it became illegal working men who had these dogs in the pit would hide the injured dogs in a pram to escape being seen, hence "nanny dog" Because also working men didn't have huge houses and gardens the very same dog would be sharing space with his children. In addition to this the men needed to be able to part the fighting dogs in the pit by getting between them. The dogs had to be able to distinguish between dog and human very quickly, very accurately and in the heat on the moment because any dog that showed aggression towards humans was no good and could not be used in the pit. As such, dogs that showed aggression towards humans were culled and not bred from. Thus, Staffordshire Bull terriers are excellent with people. One of the very few breeds where any aggression towards humans was actively bred out.
A KC reg pure bred staff should be small, short legs, and weigh no more that about 15kg. Twenty years ago people were breeding between pitbulls and Staffs. Pitbulls were made illegal. Not only do these longer legged, heavier built dogs possibly have pitbull in their lineage but these dogs appealed to a certain subsection of society that wanted big musclebound heavy intimidating looking dogs. These dogs are not Staffordshire bull terriers, but strangely in dog circles these dogs have actually been accepted as such. And I wouldn't have one of these new staff dogs around children.
I have had bull breed dogs all my life, various breeds and cross breeds. KC reg Staffordshire, Boston or Boxer make great family pets. Other bull breeds not so much, and it would be idiotic in the extreme to take on a bull breed dog of unknown breeding when you have young children.