The puzzle is simple but fun XD
But, sadly the kids only used to grab the keys
Maybe you can add a tight space too, so only the kid can pass, and then maybe make them get separated while solving the puzzle, then reunite again in the end. While being separated, the adult can only put something in front of him, etc, and make each of the separated way unique to their traits.
I think it will make the puzzles become more complicated and fun XD