Good on you SwampDonkey.

At three hours, you will be challenged by the 13 year olds watching the short attention span theater while you try to teach. Good luck. You might have to light a fire under them or whip out a big knife every 30 minutes or so to keep their attention.

I did something similar for a group of 4 year olds and their moms. We spent about 30-45 minutes talking and about an hour or so practicing with gear.

Here are two links:

Pack for Young Kids

Checklists & Safety Booklet

Basically, I just followed the booklet, then we went over the stuff in their packs. To this day, they still use their packs and the contents every time we have gone hiking and camping. They are six now. I am not sure if it will help you as your group of kids is older, but if it does help, then great. And if not, just ignore it.