Problem is shit don't stick to minors, they can not be held legally responsible because of their age (probably why so many see themselves as invincible at times). And when was the last time you've seen or heard a soccer mom disciplining her child?
Can't retailers have a clause that all legal responsibility ends after selling airsoft guns to 18+ individuals meaning whatever they do with it afterwards like handing it over to a minor, said retailer can't be punished by the law. Doesn't do much to protect the sport but at least it puts more emphasis on the actions of the purchaser. I honestly don't think there is a way to detect straw purchases unless it was in plain sight.
"Hey I'm the first one to say its a great country but its a straaaaange culture. This is a place where gun store owners are given a list of stolen credit cards but not a list of CRIMINALS and MANIACS. And now they're thinking of banning toy guns...AND THEY'RE GONNA KEEP THE F**KING REAL ONES!"
-George Carlin 1937 - 2008 (RIP buddy)