Illinois has what I perceive to be a pretty good knife law. They don't limit what you can carry - for the most part (some silly restrictions such as daggers), but if you use it while committing a felony, then it may be considered a lethal weapon.

That said, a minor puchasing a knife could - depending on their intent - be purchasing a weapon. Yeah, I know that sounds kind of "out there".

I don't know if this is law or store policy, but being the parent of two fine young kids (very responsible, both in Scouting, both taught knife safety since Cub Scouts - even though one is a young lady - she was taught at the same time as my son), I like that the law or policy would have me, as a parent, involved in the purchase. I know my children, and I wouldn't hesitate to approve a purchase, but they allow me to make that decision.