I imagine the Luke figure batting fire toward the walker would be the best bet for about a second of footage followed by laughter. If Luke vanished without reappearing it may seem like the children are laughing at the defeat of this traitorous Jedi figure.
I definitely like that idea as well. For the “disappearing act” perhaps have him reappear after the laser/fire has been dodged?
Your idea is probably the easiest to execute, though.