Hi! You should talk with a vet because momma cat cleans her babies regularly by licking them so that they will learn how to urinate. My sister(she works for a vet) and has hand-raised several litters. She says you can use a warm wet washcloth to clean the kitten to imitate what the mom does. A three week kitten may already been taking care of itself but I would check with a vet just in case. Chris