A Pit Bull????? As a family dog?????? You're joking, right?
A BULLDOG is a lovely pet. a PIT BULL is a breed developed mainly for fighting, known to be short-tempered, not good around kids, and downright dangerous.
AFAIK you need a special licence to own one over here.
I wuold recommend a German Shepherd, if you are willing to take the time to train it properly - unless you firmly make sure they know you are boss and take them to training once or twice a week for several months when you first get them, they can have a nasty dominant streak. Or a golden Retriever. These last are very nice.
Get in touch with the Kennel Club about breed associations. Also, your local branch of the SPCA will be able to tell you the same.