so now, the lift operators earning $7/hour are going to be responsible for monitoring every person (and identifying potential minors from a distance) who gets off the chairlift and play snow-security? And the guy at the bottom is he going to stop the chairlift from running so he can chase down some kid and ask for ID? How will he know who to ask? What if the kid has his helmet back on by that time? What if the kid traverses and goes to a different chairlift? I do not think it is nearly as "simple" as you want it to be.
Also, on a related note: where I'm from, snowboard "leash" is also required by law. Only one of the 5 or 6 ski areas that I visit regularly makes any effort to enforce this, sure a helmet is far more prominent than a leash, but it just shows that just because something is codified as "law" doesn't mean that the resorts really will do a diligent job policing it.