You should immediatly go purchase a milk replacement supplement from a vet or your local pet store. You will have to hand feed all of the kittens with a bottle or a syringe.
Until they are 4 weeks or older, you will likely have to hand bottle feed each kitten every 4 hours. Your local vet or humane society will be able to tell you over the phone a good brand and quantity to feed them.
You can go to a pet store and buy the milk made for kittens and a small bottle and feed them your self. They eat quite a bit so you have to feed them often through out the day as they are growing and need the nutrients to get stronger.