Dr. Seuss' The Cat in the Hat (2003)

Conrad and Sally Walden ('Spencer Breslin' (qv) and 'Dakota Fanning' (qv)) are home alone with their pet fish. It is raining outside, and there is nothing to do. Until The Cat in the Hat ('Mike Myers' (qv)) walks in the front door. He introduces them to their imagination, and at first it's all fun and games, until things get out of hand, and The Cat must go, go, go, before their parents get back.