That is a very bold statement, given that mild cases are less likely to be recorded in official data sets, affecting the denominator much more for younger people than older people.
What we do know is that a total of 412 people between the ages 0-17 are known to have died from Covid19 in the U.S. since January 1, 2020. Total deaths from all causes in that age group was 55,352 for the same period and the total number of Covid19 deaths in the U.S. for the same period was 643,858. Out of that 502,863 were among those older than 65 years of age.
If we take your claimed death rate of 0.5% at face value, 412 deaths implies 82,400 infections. According to the U.S. Census Bureau[2], there are about 74 million people under the age of 18 in the U.S.
So, the assumption of 0.5% IFR implies that only 0.11% of those under the age of 18 got infected with Covid19 in the same time period.
Therefore, either the 0.5% IFR overestimates the actual IFR by about 500-600%, or Covid19 is just not that infectious among those younger than 18.
I am going to with the assumption that 0.5% IFR is way too high. In that case, it makes absolute sense not to disrupt the lives of young children to the extent we have already disrupted and allow them to gain natural immunity through each wave.
[1]: https://data.cdc.gov/NCHS/Provisional-COVID-19-Deaths-by-Sex...
[2]: https://www.census.gov/quickfacts/fact/table/US/PST045219