Most Labradors are great with kids, but there are exceptions. I suspect that a child dropped mine when she was a puppy, and from that day she didn't like kids. She never bit a kid, but if a kid stroke her head or back, she would growl and her neck hair would stand up.
As for bull terriers - there's no way I'd ever let one into my house, never mind close to kids. One of my friends have two (siblings), and those two are forever fighting for dominance. When they're separate they're kind and gentle, but the moment they're together they fight. I won't be surprised if he eventually ends up putting one down. My concern with a bull terrier and a small child will be - what if it decides to challenge the child's authority in the pack? Especially if you're a first-time dog owner, rather stick to a breed that allows more mistakes in training it on your part.