Most of us has our own way of making a paper airplane, usually passed down from a parent or grandparent. Some of us make pointy jet-style aircraft, others fashion planes with snubby noses and wider wings. Some plummet headfirst to the ground, others seem to float more gracefully. The permutations are literally manifold.
This makes paper airplanes a rich seam for exploring many different concepts within play. You can try out different designs and work out which one flies furthest, fastest or for longest. Does the paper you use make a difference? Can you give your plane any cargo? If so, how much? You can paint and decorate them in different ways, have races and play games.
The most important thing is to avoid using kits that come with the folds marked out and the paper pre-decorated. You might get a plane that flies perfectly, but you miss out on all the investigation and design – exactly the parts they will remember and pass down to their children one day.