I am leaning towards pinworms. Could be roundworm as the other poster suggested but they would have to be the juvenile roundworms as the adults get much larger than that. Use Google Images and see what you find.
You might want to read more on the treatment plans, in that you might have to follow up with another treatment due to the life cycles (laying eggs and rehatching). I would also use some other treatments (herbals, homepathic VER by Deseret Biologicals etc) just to make sure.