These are probably tapeworms. Take a sample to the vet to have it definitively diagnosed and treated.
You shouldn't have anything to worry about as far as your son is concerned. Tapeworms are typically transferred by ingesting fleas carrying the eggs, and as long as you dispose of the infested fecal matter there shouldn't be any problems.
I would also recommend using a flea shampoo okayed for use on young puppies to get rid of any worm infested fleas she may have. A shampoo containing Neem (again, make sure it's okay for puppies) is a good choice. Neem is an organic agent that is probably the most benign and effective bug killer we've got. Normally, if I come into contact with any flea shampoo, I itch horribly until I've had a chance to get it completely off of me in a cool shower. The Neem doesn't bother me at all. I've also never seen fleas die so quickly from a shampoo! Wonderful stuff!