I've lost track since it's been a couple of years, but the FDA would have standing if the vaccine suppliers have never converted their emergency approvals to "full" approvals. Short of that, no - I don't see what could could prevent Pfizer or Moderna supplying all the vaccine they wanted as long as someome paid for it - private insurance, OOP or whatever.
We followed the pandemic very closely in real time (my SO is a MPH) - watched all the demographic numbers from WashCo Public Health and it's true, in the absence of identifiable co-morbidity, the danger to the young was vanishingly small, and now that kids are growing up in the presence of circulating virus, probably even less so. At the time the issue around children was mostly that they were a spread vector to those around them higher at risk.