If the mom feline had fleas, then there’s a big possibility that all the kittycats will have fleas. If there was another animal in the house such as another feline, or pet dog, then once again, there’s a possibility that even though the mom feline wasn’t permitted out while she was nursing her kittycats, fleas were brought in by the other animals.
One of the very first things you must have in your house is a flea comb. As quickly as you bring the kitty house, take it to the restroom and carefully talk to it as you slide the flea comb through the cat’s fur.
In your kitty grooming box, you should have picked up something that will both kill off the fleas, and be safe for a newborn kitten. Have this ready for when you first bring kitten into your home and if you find a flea on your kitten, follow the instructions on the box or bottle. Remember that the kitten is already going to be feeling very insecure at this point, and so you must keep talking gentle to him and not frighten him more than necessary. It’s much better if you can do this on your own without any other family members/pets in the room so as to keep the environment calm. Once he’s clean, allow him to meet the rest of the family, but don’t allow him back into the cat carrier, or onto any bedding/toys that had contact with him before you did the flea treatment. Make sure that you wash these all out thoroughly before he’s allowed to have them back.
In most cases a kitten will not have fleas when it arrives in its new home, but taking a few simple precautions, so that you’re prepared “just in case” he does, will make a potentially big job painless for both you and the kitty.