I've been on a forest schools course. It was fab. They talked about the magic of having a campfire in the forest activites sometimes.
Only problem, you need a qualification to be able to satisfy the health and safety and the insurance to be able to do it with the children. Forest schools level 3 costs ££££. £800 cost, plus the cost of supply for 7 days, plus £140 for the outdoor first aid course you would need too.
My wondering thought is whether there are other similar courses I could try and find that would also suit to qualify an adult to be able to light a fire. I know the scouts/guides etc have campfires, so there must be other ways that could be a lot more affordable to the school.