I'm so sorry. Who figured fish were jumpers as WELL as swimmers?
But y'know, nearly every time I shop at Meijers I go by the Bettas, in the fish area of the pet dept. I used to have Bettas all the time, bred them, really got into them. And they're so beautiful. And when you get interested in them big time, they are unbelievable to observe. (I'm referring to the breeding process, because that in itself is a sight to see! And I'm not voyeuristic). Maybe that could be a way of making this right with your son; get a larger tank, take the necessary precautions, get a new pair of fish (make sure you read up on them first; they can't be placed together on normal bases) and observe Mother Nature. Try and make it a science project for school science fairs? Take pictures, feature the 'starring role' fishes, etc.
Good luck. And just for the record, Bettas are a little on the kookie side.