Here are Ted Wragg's tips for success.
Safety is the number one issue: Make it clear that this is not negotiable, not optional, so unreconstructed idiots cannot be allowed to take part.
Get the appropriate qualified supervision: outdoor pursuits can be very different from each other, so an expert in canoeing may be clueless about climbing.
Parental backing: ensure that parents are fully in the picture and that the ight clothing is worn; there are some sad cases of children become soaked and wearing entirely the wrong gear.
Notify the appropriate authority: always let someone - the coastguard, hostel warden - know exactly where you are going and when you expect to return, remembering that mobile phones can often be out of range in many outdoor locations, like moors and rivers.
Tire them out: the first night away can be a problem, so some old hands stop a few miles short of the hostel and everyone walks there; children will not have much appetite for a midnight pillow fight if they're knackered.