Since you are a new poster, I will not make any nasty comments about shorts in CA, when it is about 34 degerees here, LOL!
Little land sharks, yes they are.
Be consistant and calm. You can say "Eh! no bite." and remove your shorts from where he can latch on, and ignore the puppy for a few minutes. As soon as he plays rough, game over. He WANTS to play. He will learn that when he bites down, the game is over. He will get it.
A lot of people swear by the distract him to an appropriate chew object. I do not know how this would not be a reward for biting. But GSDs are generally smarter than we are and can figure out the difference even if it is not apparent to us.
When my pups are chewing, I make sure there are bones and ropes, and sometimes frozen ropes for them to work their teeth on, because they have to chew.
You can say, "Ouch, those are MY fingers, THIS is your chewie." And give him the chewie.
I also teach my pups GENTLE. I do it with a treat, and I make them take the treat NICE or GENTLE. Starting with the treat in the open palm, and as they get that, I move it to my fist, when they are good at being careful taking it from my fist, I will move it to betweein the thumb and first finger. This is a great target for dogs to get fingers too. But EVERYONE that will offer your dog a treat will do it this way. So it is good to teach him to take it GENTLE. Once they will stop themselves and noticeably be careful when taking the treat, when you remind them GENTLE.
Then you can apply GENTLE to other things, like the baby. GENTLE with the BABY. It reminde an exhuberant puppy to slow down and be careful.
Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.