1. Children don't exist in a vacuum. Even if they don't become symptomatic, they can still be a carrier and they can still infect adults that they're in contact with. Should teachers be sacrificing themselves? Should families isolate their children within the house?
2. It's a low risk to healthy children. What do you do for children with other health complications? America has a lot of diabetic children. Covid is also shown to increase the risk of pre-diabetic children becoming diabetic https://www.nbcnewyork.com/news/coronavirus/covid-19-substan...
3. Covid is not a one and done. You get it, and it can have long term lasting effects even if it doesn't kill you. That applies to children as well.
4. Covid spreads very quickly with a relatively high risk to the greater population. Lockdowns were a safety measure at the very least to be able to keep pace with things. It was absolutely the right thing to do till the virus was more understood.
5. As the virus was more understood, it reinforced the above points because covid has very complex side effects