Are these pinworms you are talking about?

You will need to get a treatment for the whole family for about a month, which will include a couple doses of medicine, one at the beginning, and one two weeks in. Eggs on surfaces can survive up to two weeks.

Also check to see who he is playing with and where. If he does go to a daycare, notify the daycare provider. Keeping his hands clean and washed and away from his mouth and face should help keep them away as well.