Some here know, and some don't that I am an ex-police K-9 "trainer" and handler. I too love big dogs. Especially German Shepherds, and Belgium Malinoises. However! What many don't understand about dogs is. The dog thinks like a dog. Sure he's friendly to the hand that feeds him, but many dogs see themselves climbing to the top of the pack order by dominating their sibling pack members. i.e. the wife, if she is a little shaky with the big dog, the children, and VISITING CHILDREN. This is where you get into trouble with breeds like the pit bulls, rotties ect.
When I was picking prospective police dog pups, I broke them down into three drives. Prey, Social, and Defensive drives. PREY DRIVE, is what causes a dog to WANT TO CHASE A BALL. It is an instinct that is very strong in most pit bulls, and there is nothing like a running, screaming, bunch of little kids to TRIGGER THAT DRIVE, which sometimes causes, and otherwise friendly dog to go to far. They can no more help it, than wagging their tail when their happy to see you.
You may not like that fact, and some will not accept it, but lets just say, that I truly hope you get away with that attitude for the "children's sake" and others "outside the family", to quote Hillary.
My personal patrol dogs were SOCIALIZED to my family, but there were boundries set, that my family knew, and the K-9 was never completely trusted. An example was: We had a crab apple tree in our front yard. The blue grass in our yard was lush due to my watering and care. In the evenings, the family many times would go out and lay around in the yard, joking and playing. One year I forgot to have the blooms sprayed, and we got crab apples. YUK! My wife picked one up, and threw it at me. The K-9 went and laid down in front of her. She thought that was kinda neat, so she threw another. This time, he laid AGAINST her, but showed no signs of aggression, but some stress. She still thought it was a game, and threw another. He nipped her, and the game was over.