perscription sports goggles worked great.... my son had them when he was young and they survived gym class and karate, sledding, skiing, etc.
a word of warning. You want to get the kind that have venting or open areas on the side or they fog up when the wearer gets sweaty. Just remember that this kind, though you can wear them swimming, does not keep water out of your eyes. Kids sometimes mistakenly believe they are swim goggles. I wear them, too, for sports, and you can swim in them( If I can't see, I can't supervise my children), but water does get in your eyes. Overall, money well spent. Children on the sidelines because they can't see or are timid for fear of breaking their glasses, or clumsy because they take their glasses off have very little fun.
Another related tip.... if you spend a bit more and get the flex-frame glasses (titanium frames is one option), you will be able to have them re-adjusted when the normal boy rough and tumble bends them out of shape, instead of replacing ones that break.
take care, L.