- That 3Dslash app looks ideal for kids. In fact it looks like so much fun i downloaded it myself to give it a try.
- If you had a very small printer running during part of the presentation, it might help the kids to visualize the process. Probably not necessary, but might generate a bit more excitement. The printer wouldn't have to finish the part necessarily.
- You could try to find local printing services, through 3Dhubs, Makexyz, or Sourcemake to help the kids get their models printed after the workshop.

I wish i could offer something more, but it looks from your slideshow that you have the situation well thought out.

Best of luck.