How can I protect my kids' toes from this evil grating in the floor?
If the grate is easily removable, simply lift it up and wrap it in a thin, loose fiber fabric like a muslin, cheese cloth or nice smooth burlap. (not the rough course kind). Even a piece of regular fiberglass screen would do the same thing.  This will look nice, let plenty of air through, keep excessive amounts of dirt out of duct work and help protect little piggies. Check out the fabric dept at Wally World, bet you can find what you need for a couple of bucks.