Alvin's Solo Flight (1961)

Tubby invites Little Lulu to join him at the beach, but Lulu has already promised to mind Alvin that day. Tubby reluctantly allows Lulu to bring the little pest along with them. While at the beach, Alvin does nothing but complain about being hungry. A grumbling Alvin agrees to bury Tubby in the sand, but then he bites Tubby's toe and complains again about wanting food. Lulu gives Tubby twenty cents to buy a hot dog that he and Alvin can share. At the hot dog stand, Tubby buys a dog with mustard and sauerkraut and then eats his half. But before he can hand Alvin the other half, the little boy has disappeared. Lulu and Tubby go looking for him at the Lost Children Station. The place is filled with boys and girls, but Alvin is not there, and the attendant won't let them bring back another boy who is a lot nicer. Meanwhile, Alvin is with the balloon vendor. The small boy steals some helium balloons, which sends him flying into the air. Later, when Lulu and Tubby are sure they've lost their charge for good, they find him up a tree. Since they don't see the balloons, they refuse to believe Alvin's story about he got back home: "I flew!"