"Please let me down"

According to an on-line search, the suppliant on the teeter-totter no longer seems to call upon Mister Mustard, but upon Charlie Brown, Farmer Brown, or Mrs. Brown. "Mister Mustard, Mister Mustard, please let me down" was for those times when a heavier kid kept a lighter-weight one up in the air on a teeter-totter and then demanded a reward for bringing the one aloft back down to terra firma, with no promises that the descent wouldn't be an abrupt one. A homemade teeter-totter (and we didn't use the world see-saw, although we knew from the nursery rhyme that they're one and the same) can take you very high indeed. There were those among the grown-ups who were fond of saying, "Let that be a lesson to you." Here, a possible lesson might be to be sure before you ride together that you know who's on the other end of the tilt-board and that you can trust that person to let you down and to let you down gently.