Idea for a book?
Eighteenth century Europe. A merchant brings a kite home from a trading expedition to China and gives it to his son. When one of the children gets lost in the mountains, the boy, taking inspiration from a kestrel, builds a kite big enough the carry him and, with his friends flying it, is able to spot and rescue the missing child. Kite flying then becomes a popular past time in the town, with constructions becoming increasingly elaborate. This comes in useful when an invading army tries to attack them and the children become a sort of proto-airforce, flying kites to drop grenades on the invaders and drive them away, saving the town.