I’m not sure how it’s legal or ethical to test the COVID vaccine on children, but it’s about to happen

Pfizer’s COVID vaccine trial for kids is “fully enrolled”. Children don’t possess the legal ability to give informed consent, so how is this possible? The full trial for the vaccine in adults isn’t even over, as researchers are gathering data on the vaccine as it’s being administered among the general public. Everyone getting injected is a part of the trial, whether they know it or not. So, I’m completely flabbergasted as to how so few people are demanding the brakes be applied immediately on this rush to vaccinate children with an experimental, never-before-attempted, mRNA vaccine, for an infection that does not pose a risk to them.