Good luck to your boy and his team in their future endeavours. My mates and I used to make bottle rockets with varying degrees of success, but we could never get them to fall back to Earth too gently. Most landed with a thud, which some didn't appreciate, particularly if it landed on their flower beds and wrecked the roses, etc.
The other thing we used to make, which had a scientific background but had nothing to do with science projects, and was infinitely more dangerous, was weedkiller and sugar bombs. This was England back in the 60's... and there was heaps of shit the Germans had missed to blow up. well that was our thinking at the time. In one case we made a 10 gallon one and put it in an old air raid shelter we discovered in the woods miles from anywhere - what a funny place to put an air raid shelter... only the see the 12' x 12' x 14 inch thick reinforced concrete roof get thrown 10 feet or more in the air.
It was pretty potent stuff, and now I look back on it, it's amazing any of us survived, given the crazy pranks we pulled with it. Not that we damaged peoples property, anything that was important or would be missed, but we blew up a lot of shit... like this old house that was condemned shortly after the war but nobody ever got around to it. After we'd finished with it there was nothing but rubble. We had some fun and no harm was done... 'cept maybe putting a demolition team out of a day's work... hehe, should've got there sooner ya lazy bastards.
Hmmm, we were pretty pissed when they took out the various ingredients that allowed the weedkiller and sugar to detonate, but it was probably a good thing. No probably about it! That move saved our lives and many others, me thinks... cos kids today can't do the crazy shit we did with it.