It is a small cage, barely large enough to fit the child its holding, with iron bars and many padlocks. Vicky's version of the box is suspended over a pit, and falls into the pit when she places the heavy padlocks on top of the cage.
In the episode Baby Face, Timmy wishes himself into a baby to avoid Francis beating him up, but Francis finds him as a baby and tries to beat him up anyway. Francis is stopped just in time by Happy Peppy Gary and Betty, who sing a short song and lock Francis into the cage while other horrified children look on. Later, at the end of the episode, Timmy is returned to Vicky's care, who uses the Fun Box to get revenge on Timmy for wishing her head into a fish.