This 21 May 2020 video says about itself:
Coronavirus: Elite Sydney school shut after positive COVID-19 test | Nine News Australia
New South Wales Education Treasurer Mark Scott discusses the closure of an elite Sydney boys’ school after a student tested positive to COVID-19.
Translated from Dutch NOS radio today:
The case at primary school De Veldhof came to light when a teacher turned out to be infected. The three other infections emerged from source and contact investigations. …
All parents have been informed about the infections. As long as their children don’t show symptoms of Covid-19, they can just go to school.
If a person shows symptoms of COVID-19, then it may already be too late. At first sight healthy people, not showing symptoms (yet) may infect others.
Newly born baby in South Africa dies from COVID-19: here.