My female Krystal just had her puppies and I find a flea on one of my males!

I'm absolutely sure I'm not putting any flea product on Krystal but don't know what else to do for her protection and the puppies. I have never had fleas with Krystal, Jack, or Morgan since I got them and didn't have to use anything. But we finally have new neighbors in the house next door that has been vacant for awhile and they have two large dogs. And I'm speculating that the fleas have traveled from yard to yard. How about some advice from yorkie owners that have had to deal with fleas. I could use some. the puppies go in for their dew claws and tails tomorrow so I will be asking the vet too! Thanks for any input!
Dion