Bring a scale. As an Eagle Scout, former Assistant Scoutmaster, and soon to be Tiger cub parent that piece of advice (from this site) was a revelation. Knowing, rather than thinking, what things weigh makes a difference.

Feeling the difference of picking up your pack, and picking up one of theirs, will make a difference. Ask the Scoutmaster to bring his pack and have a couple of the older boys (who are about your size) load and bring theirs.

For the younger boys and their parents, seeing cheap ways to make backpacking more enjoyable, and being able to make gear for low cost that lightens load will penetrate. Explaining costs and benefits will penetrate.

Explain the cost/quality/weight dilema, and how you approach it. The boys parents have to buy (and replace) a lot of their gear, particularly clothing, regularly.

You wouldn't have been invited if some members of the troop leadership didn't see an issue with what they or their boys were carrying, or didn't have a future program in mind that would require lightening up.

I can see the liquid fuel rules being... risk adverse. In the early 90's, the boys weren't really allowed to start up liquid fueled stoves. We did all our cooking on open fires.