Richard, unless your son could tear up an anvil with a rubber hammer, there's little he could have done to break the spring.
They're made of metal that, even though it's designed to flex, will ultimately fail. That is not your son's fault.
The spring was broken on my 152 and I just lived with it. I even bought a new spring, but never felt crazy enough to drill out the hinge and install the new spring.
They're not very expensive, either. The labor to replace it and then to touch up the paint on the rivets really makes it hard to justify when the only manifested problem is that it won't hold itself up. But, if you want to fix it, it ought to be less than 200 dollars for a turn-key repair.