Getting bitten in the face by a pit mix and not breaking skin sounds like maybe the luckiest thing ever. Not quite sure how that happened. One or three ragdoll shakes will usually just lacerate the **** out of everything.
Not being a tough guy or anything, but I carry a folding boxcutter like this on me at all times:
and the main reason is in case of a dog attack like what happened to you. The plan is to either poke their eye(s), slit their neck, or just open up their belly and let their guts fall out as they stumble around. Whatever it takes to get them off the victim.
The sad fact is, in cases like LFS's if that dog locks on and doesn't want to let go you are ****ed if you don't have an immediate answer. Often times the damage is already done too.
So lucky LFS, but your son is going to probably be freaked out by dogs for the rest of his life now. Better than the alternative I guess.