Repetition for Learning: The Preschool Years

How much repetition is enough repetition I wonder? Chase is four and one-half. He knows his colors, numbers, alphabet and sounds, how to print his name, etc.

We had been working on these things in the past school year. I definitely want to take a break from formal learning this summer but I do not want Chase forgetting what he has learned.

When I try to get him to go over something he has already learned, he does not want to. "Mommy, I already know that!" he says.

What creative ways have you moms used to reinforce skills that seem more fun than repetitive? Is it even important at this age to have the repetition and reinforcement?

Thanks for your help.