I've taught a lot of folks to make fire. I find it's honestly easiser to have one set that you know really works for you to demonstrate and to work one on one with, and another two (or if you're working with scout patrols, or school (table) groups, one set for each of those to play around with.
Once they see it in action, understand the how and why of it working, then encourage them to use the materials provided and see if they can make a set themselves.
It an all too easily become an overwhelming and frustrating experience trying to herd up to thirty kids all at once.
Best advice it to get the leaders involved right from the start
A patrol is six kids, that's manageable to get them from a standing start to making fire in a reasonable time.
It's worthwhile, I found, to provide several kinds of firelighting kits too. From flint and steel to handspindles. The 'pump' drill works well too, and that appeals to many of them.
Basically I just made sure I had masses of hands on stuff for them to experiment with. Lots of tinders, lots of interesting materials.
Mugwort is a very satisfying blow up an ember into flame type thing. Billowing white smoke.
A big fomes with a really hot ember in it lets you carry fire for hours
Blow on it and it'll glow fiery red.
Chagga is superb too.
All good stuff
I hope you have fun doing it
Up here I need a special certificate that proves I am of sound character (no criminal issues) etc., from Disclosure Scotland ...a PVG certificate.
Information about the PVG scheme, the types of work it applies to, and what a PVG disclosure shows.
www.mygov.scot
to work with children, and to be covered with my public liability insurance.
I'm not sure how the Scout Association handles non leaders working with the scouts elsewhere.