Robbie Larsen is a young gymnastic prodigy and the only son of the Larsens. While on a vacation with his parents to the South Pacific, he becomes overwhelmed by his excessive Olympic training and flees to the The Castaways Resort, where he hides in the jungle. Slipping into the resort to steal food from the Skipper at the Snack Shack, he's discovered and befriended by Gilligan, who helps hide him. The Skipper, meanwhile, finds out Gilligan has been hiding Robbie from his parents coming ashore in search of him. Confessing to the pressure he felt, Robbie and his parents reconciled afterward.
- Robbie was played by young actor Ronnie Scribner.