I work on a similar sized fleet of bikes for our local Cub Scout camp. The Cubs (about 10 years old max) do not trash them to that degree. Most of the trails we ride are traversable (spelling?) by the camp trucks.

They tried bikes on the Boy Scout side of the camp, and they all got trashed in various ways.

So they ended that program. I don't want to say that they replaced the bikes with ATVs because that's not necessarily the best way to look at it, but they did end their bike program and then start up an ATV program. Scouts need to be 14 to ride the ATVs. Those require maintenance too, but they don't get "trashed" because they ride with a lot of supervision.