Social Isolation had nothing to do with it. Lets not pretend kids arent out playing with friends, soccer, or even protesting without a mask.
Well at least you now know COVID is safer for children 17 and under compared to the flu (With a vaccine). Time to open up schools and sports.
A lot of diseases are less severe in prepubescent childhood, like chicken pox, mumps, some types of measles. Some diseases are not less severe. Since this is, by definition, the first year of research and health statistics for Covid-19, no one knows which group it is in.