I think my cat had her kittens and I can not find them, what do I do?

If she did have them you will start to hear their cries very, very soon. Cats like to find a secluded place to have their babies so they can keep them safe and private. You might want to keep an eye on her, look to see where she goes often...they might be in the room that you mentioned behind stuff, under a bed, in a closet, places like that. Good look in finding them :D