We haven't gone to a theme park at all with our kids yet, but I always thank servers at restaurants, people who hold doors, etc., and my DS (age 3) apparently noticed, because when we eat out, he thanks the server when they take our order, bring our drinks, bring our food, and check on us. He thanks almost everyone he comes in contact with as well, the cashiers at the store, whoever, and he tells them "Hab a good day!"