What's delta like for under 16?

In the US through May 2021, so it might not be a good representation for delta, here were the infections, hospitalizations, and deaths per 100k for various age groups:

    Age Inf Hosp Deaths
   0-17 37k  287    0.5
  18-49 44k 1100   25
  50-64 32k 2600   85
  65+   22k 5200 1140

Unless the numbers for delta are way higher, that suggests that for under 17 getting your immunity by actually getting COVID is fine. The main reason then you want to prevent kids from getting COVID is not so much for its danger to them but rather for the danger to the adults that the kids will spread it to. Kid gives it to a grandparent, and that grandparent is 20x as likely to be hospitalized and 2000x as likely to die as the kid. If the kid gives it to their parents, the parents are 4x as likely to be hospitalized and 50x as likely to die.

If the numbers for delta are at all similar for kids, then there is a good chance that there is not much difference between a population where everybody gets vaccinated and population where all the adults get vaccinated but the kids do not, suggesting vaccinating adults should be the priority.

The long term endgame is probably a population where it is endemic, everyone gets it as a child when they are young enough that it doesn't cause serious illness, and then keeps getting it every year or so for the rest of their lives. Those subsequent cases don't cause serious illness because they still have protection from the last time.

That's what happened with the four other coronaviruses that are in wide circulations in humans. They are thought to have caused terrible pandemics when they first got to humans which were deadly in adults but not bad in children. Nowadays they are still around, everyone gets them frequently, and we don't even bother to have a separate name for the illness they cause. We just lump it in with the illnesses from a bunch of other viruses and call it the common cold. Around 20% of common colds are from those coronaviruses.