Getting sick less often? Maybe avoiding norovirus or some cold viruses? Maybe avoiding the flu (on quick search, influenza’s transmission mechanism is not entirely clear, but the flu can be very nasty in small children)?

One might reasonably debate whether it’s beneficial to a small child, and how much, to get sick less often. And one might reasonably debate the tradeoff between that benefit and the down sides of wearing a mask (e.g. more difficult communication). And one might extremely reasonably debate whether any of this would or could justify requiring other people’s children to wear masks.