Yes, C engines are too powerful for Cubs, and we recommend 1/2A, A, and maybe B engines for beginner flights. With these engines, rockets will fly high, but not too high, and the scouts get their prized possession back.
Do you have a recommendation for a complete setup for a 40 Cub Scout event to allow each cub to launch twice in a couple of hours?
For a group that size, we recommend at least 2-3 launch pads. There is great fun in lining up the rockets side by side so the scouts can see which one will go the highest. In terms of kits, the Estes Alpha III bulk pack and the Estes E2X Generic bulk packs are among our most popular for your type of group.