Wish people like @colinbraziersky would stop amplifying the inane binary "your child is more likely to be hit by a bus" nonsense. It would only be a valid comparison if Covid had somehow REPLACED being hit by a bus as a risk AND you could INFECT YOUR NAN with being hit by a bus.
It's just not how risk works. Engineers checking an aeroplane before take-off, don't go "I'm not going to check the landing gear, because a flock of geese might fly into the engine". We take a reasonable amount of action to forestall EACH risk.
We teach children to be careful crossing a road and look both ways, to reduce the chances of an accident. In precisely the same way, we can teach them social distancing and mask use during a pandemic. We cannot eliminate risk, but we can mitigate each risk as best we can.