As in, outside of the social bubble. Usually pre-school kids still have fairly active 'social calendars', with nursery, parent/child meetups, being dragged to family events. COVID stopped these, which stopped transmission.

In some places in the world you literally cannot go outside. We've been stuck inside for 4 weeks right now in Da Nang, Vietnam. We can go to the balcony, but that doesn't count, of course.