four month old german shepherd puppy that is fearful of all but owner of three weeks

Question
my four month old german shepherd puppy is fearful of anyone other than myself.  i live with my highschool age son who has virtually no contact with the pup and my college age daughter comes home on the weekends.  he will hide under tables, behind the couch, etc.  when i have tried to get my daughter to walk him on lead, because that is the only way she can get near him, he panics and runs up on the porch.  when she approaches him there he growls and barks at her.
he is of american bloodlines, the dogs at the kennel all seemed friendly and i have experience with mainly german lines and have not had problem one before this.  help!

Answer
This has nothing to do with bloodlines and everything to do with socialization. Type alpha boot camp into your webbrowser and try to do everything they suggest. Meanwhile WALK YOUR DOG daily twice daily for at least thirty minutes each time BRISKLY with puppy at heel. Get this puppy into a puppy socialization class, take him everywhere you go that you can POSSIBLY take him,expose him to everything and don't baby him through anything. If you do the oh poor baby it's ok thing you are reinforcing his behavior. I can't possibly work you through this in just one post but if you go to the site I suggested and if possible get Cesar Milan's Be The Pack Leader book, you can work through this. Stop it now before you end up with a fear biter on your hands,.
Good luck
Cindi