shelters from forest materials are fun, but realistically carrying a small tarp and some paracord with the knowledge of proper knots to rig it up tight is lots of fun and more practical, use knife skills to cut and notch some tent stakes from sticks

I'd suggest some basic knots and a tarp setup exercise.

build tinder bundles.

You could also make char cloth over a fire. After its done, pass out a square to each kid and have a contest to to strike sparks into the char cloth from the back of an axe or some other carbon steel with a rock. throw into tinder bundle and get flame!

set flame under a fire lay w/ pot filled with water handing on a tripod, first team to get a rolling boil wins. have an adult lead each team and get kids to assist in building tripod, hanging apparatus (use knife to whittle a hanging hook), firelay etc.

make some slings (paracord, leather patch http://slinging.org/index.php?page=making-a-simple-sling-an-illustrated-guide) and teach kids (safely) how to sling rocks (maybe into a lake or something) this is lots of fun! primitive hunting tool.

make a simple orienteering course to teach compass / map skills

hide a "geocache" to teach GPS skills

definitely make simple traps like the figure four deadfall to practice precision whittling skills

show them how to properly sharpen knives

bring some slingshots - more projectile fun