I'm guessing returning him isnt an option?? Its really too early to be away from mom.
I'd also get him to the vet asap. he's probably going to need to be treated for tapeworms etc.
In the meantime, peppermint castille soap is very gentle lather him up and let it sit for 5 full minutes. then rinse well. be sure to keep him warm and comb completely with a flea comb. If you dont have a flea comb handy, you can use a lice comb which should be available at any 24h drugstore.
food grade diamatious earth helps kill fleas and is safe. Sprinkle around the house, in his bed and sleeping spots and anywhere in the car he's been.