Lilly and Leon had accumulated a lot of cardboard boxes after moving. Instead of trashing the boxes, they decided to use them for Cardboard Box Office, where they recreate famous movies scenes. This is awesome.
This is in reference to a child's song called little kittens" The 3 little kittens lost their mittens and their mother refused to give them pie. When they found their mittens the mother then allowed them to have their pie!