I understand your view but imagine that the opposite was found, that children were infected the first time without symptom, but the 2nd time it became lethal, because of antibody-dependent enhancement, (ADE) which happens with Dengue hemmorhagic fever.

It can be a problem with Zika (remember that new virus which destroys fetal brains) and with RSV (early vaccines caused a worse reaction upon natural infection). HIV may operate as a ADE virus.

There are several respiratory viruses which can have ADE - like the flu. Remember SARS? MERS? (Early 2000's) - they are related to COVID and were observed in animal models to create ADE.

I rember discussion at the beginning of COVID that nonsymptomatic infection may result in more severe COVID on reinfection by a variant via ADE. Children were thought to be mostly asymptomatic.

So you can see the fear that children which had asymptomatic infections could boomerang. We now understand that is not true for COVID and its variants.

(It also is an amusing variation on the idea that vaccinations are an unalloyed blessing. Sometimes the antibodies produced by weak vaccines allow viruses which bind to the antibody to be absorbed like a Trojan horse into immune cells and become quite virulent.)

So, I understand her view and I share then feeling that by end 2021 all major infectious paths had been traversed for COVID and children were not developing ADE. That should have been an immediate exit criteria for remote schooling but it went on too long.