Big John, Little John is a barely-remembered live-action Saturday morning kids' show from the 1976-77 season; it featured the misadventures of John Martin, a schoolteacher who takes a sip from the fountain of youth and thereafter - every time he's splashed by water - reverts to being a 12-year-old again. His wife and son know of his affliction, and even tried to cover things up by claiming that Little John was actually Big John's nephew. Naturally, John would find himself doused with water at the most inappropriate moments, and all sorts of shenanigans would happen as a result of trying to keep his odd condition a secret.
The show's adults were played by good-old early-70's-TV stalwarts Herb Edelman and Joyce Bulifant, who appeared occasionally on The Mary Tyler Moore Show; Little John was played by Robbie Rist, better known as Cousin Oliver from later episodes of the Brady Bunch (the show was executive-produced by Sherwood Schwartz, who must have enjoyed Rist's Oliver interpretation enough to re-hire him). The show didn't do well, however, and only lasted the one season. I just barely remember it myself; but for some reason the theme song has stayed with me all those years...
Big John Martin - Herb Edelman
Little John Martin - Robbie Rist
Marjorie Martin - Joyce Bulifant
Ricky Martin - Mike Darnell
Miss Bertha Bottomly - Olive Dunbar
Homer - Kristoff St. John
Valerie - Cari Anne Walker
Stanley - Stephen Cassidy