The Kingdom of Youth is a land in the Super Mario Bros. Super Show!. The Kingdom of Youth appears in only one episode, "Two Plumbers and a Baby" and is full of giant blocks (that kids play with) and other things babies like. The center of this land has the Fountain of Youth a machine that makes anyone, any age. Mario, Luigi, Princess Toadstool and Toad came here, only to be attacked by King Goo Goo Ga Ga Koopa and get the princess turned into a baby.
Baby Park from Mario Kart: Double Dash!! and Mario Kart DS seems to take place here, even thought it looks more like it takes place on Yoshi's Island.