I came here with the same question a few months ago. The best advice I got, I can't even remember which member gave it to me, was that it's normal, they eventually outgrow it, and "they don't call them land sharks for nothing." lol Get tons of chew toys, make sure he has one in his mouth ALL the time. I'm not joking.
Good news is those razor sharp teeth will fall out, at about 4-5 months. The adult teeth that come in hurt much less. But what's really important to know is that your pup is completely normal. Buddy is 10 months old and has learned bite inhibition, but is still mouthy when he gets excited in his play. He now "nibbles" with his front teeth, because he doesn't want to hurt us with those gigantor back molars, but the nibbling really pinches, too. So we still have some work to do with him.
One of the many things I've learned from Buddy is that he mirrors my emotions exactly. So the number one thing is to stay calm. The calmer the person is who is playing/handling him, the calmer he will be. When you popped him on the rear, he ramped up only because you ramped up. He was meeting your emotions, most likely thinking you wanted to play. The more upset you get, the more crazed he will get. This is not aggression, it is just the way he is wired. So stay as calm as you can. When he starts to mouth you or the kids, plop a toy in his mouth. If he mouths too hard, whimper like a puppy would and walk away, completely ignoring him.
But the biggest advice I have, as you probably already guessed, is to make sure the puppy always has a toy in his mouth.