Entry requirements for US citizens
US citizens need a valid passport and the electronic C-5 immigration and customs declaration; no visa is needed for stays up to 90 days.
The US State Department says to complete the Electronic C-5 form before traveling, as border officials may not allow entry without pre-approval. Your passport must be valid when you enter and when you leave. Carry proof of relationship or a consent letter when traveling with children and one parent is absent.