I heard a few months ago that UK infant ICU was in a dangerous spot because babies had caught all the bugs. Someone born in March 2020 would hardly have been outside until they were 1, so would be getting their first exposure to respiratory illnesses late. Babies usually get a slow, trickling exposure. By getting exposed to so many minor illnesses at once, their immune systems overloaded and they ended up in ICU with 4 or 5 things at once.
No firm data, my mother is high up in UK health policy so I heard from her.
The best thing for your child is for them to socialise as much as possible with other kids. That means they will get sick. In normal times, 2-3% of babies end up in hospital with respiratory infections at some point. Obviously in the short run it sucks, but long run it's healthy.
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.
