• The first case of Covid in the US was January 20, 2020.  The Moderna trials in humans began March 16, 2020.
• Now you are considering mandating a set of vaccines that in addition to short development times also had a short (although broad) testing time.  The vaccines are already proving to be less long-lasting than previously thought, requiring boosters. 
• The most at-risk portions of the population are already largely vaccinated. 
• If the fatality rate for children were around 2% or so a mandate might make sense, but with the current facts it simply doesn't.

Source first US case: https://www.ajmc.com/view/a-timeline-of-covid19-developments-in-2020

Source Moderna trials: https://www.biospace.com/article/moderna-s-covid-19-vaccine-clinical-trial-starts-today/

Source child covid: https://data.cdc.gov/NCHS/Provisional-COVID-19-Deaths-by-Sex-and-Age/9bhg-hcku