By age there have been 11 deaths under the age of 1 from COVID, 9 deaths between 1-4 years old, and 16 between 5-14. So 36 deaths nationally for people under the age of 14. Total deaths this year out of that age group are 11,998. https://data.cdc.gov/widgets/9bhg-hcku
But to your point on percentages, deaths over known cases by age group, I can't seem to find data by age on who catches other than through the Texas website. Extrapolating that data and applying to the 4mm number of national known cases, around 5% of cases are under 14. That ends up being a death percentage of .018%. Or 1 out of 5,555. Problem is, we know we have massively undercounted cases by 10x? 20x? so it could be 1 out of 11,000 to 1 out of 22,000.
To further that point, if 100% of the population got it and those numbers above hold, you'd have anywhere between 2500 and 11000 deaths of kids under 14 from COVID given we have about 61mm people under the age of 14 in the US.