Jon, While not teaching the trick would be preferable, you will find the older kids won't be able to do it anyway.
Some years ago I was asked to give a talk on magic to gifted children and as part of it I decided to teach them a simple self-working card trick. I wrote to a playing card manufacturer who donated a couple of dozen decks. The trick was based on a simple force.
The ages were eight to fourteen - and these were Mensa type kids. Only one of them could grasp the concept and that was the eight year old.
Now you could explain it away by saying I have terrible teaching skills but I think the bottom line is that even if they do grasp it, they will have forgotten it the next day.
And who knows, it is possible one of them might develop an interest in magic.