Not a fan of lockout keys cause really kids shouldn't even be able to even get their hands on the guns they should be locked up. Instead of the hassle of finding a replacement key at the very least go to any sporting goods store and buy a security lock box, then you'll also have something for the car too.
Hornady Keylock Safe 2700KL 1 Gun Pistol Vault - Black
Hornady Keylock Safe 2700KL -Exceeds ASTM International safety standards for child and pry resistance, lock strength, drop/pick/saw tests and hinge attack resistance.
www.sportsmans.com