This is especially striking with children: if the US had the same number of covid infections as seasonal flu, you'd probably have lower pediatric deaths from covid than flu.
What you should be comparing is case fatality rates.
You have to compare just the case fatality rate. Comparing fatality ratios alone is too likely to measure unrelated factors.
Anyway, here's some IFR estimations for covid by Imperial college: https://www.thelancet.com/journals/laninf/article/PIIS1473-3...
You see significantly higher multipliers by age group than for flu. As one example, they are guessing teenagers have 1/17th the mortality rate of say a 40 year old. For flu (going by deaths), it's about 1/5th.
Sweden and Iceland never closed schools for young kids. Data doesn't look any different.
The caveat is that mortality rate is intimately tied with the availability of certain types of care; if you need a vent and the hospital is full, you die even if otherwise you would’ve lived. Thus case mortality rate will change dramatically once the hospitals fill up.