outside or inside of lens? if its on the outside that shit you can buy in the store to fix scratched glasses works although i would be careful with this method. seeing as you are handing em down though i would say go for it.
To protect scratches to goggles in the first place, use Goggle Guards, available at Goggle Guards - Home
They are a soft fleece wrap design that protects lenses on both sides. They also prevent the strap buckle from scratching the inside of the lenses while stored in one of those bags. This happened to me!
Another benefit is that they can protect your goggle while not in use and resting on your helmet !