My staffy x ? pup displayed this behaviour in the early days. She was a rescue who had been badly handled. We got her at 6 weeks and she snapped her way through the first 3 weeks at my kids aged 4 and 9. At the end of my tether, (debating whether to give her up) I got professional advice and some good strong training (for me and the kids more than the dog, to be honest) did the trick, Now she is very good with the kids (she is now 6 months old) but still requires firm consistent training (so do the kids BTW) I was advised about the dominance issue, get the kids to feed her, feed her last, wait outside the door till everyone else in etc. its working for me. Good luck with pup.