We homeschool and live below 35N. Recess is every day at 11:30 for ~20 min. Just like when I was in school in the stone age. Unless it’s below 40, over 100 or raining. Haven’t had the kids D tested though. We’re part NA so they’re darkish to begin with. Our ENT suggested the D3 in olive oil drops if you can believe it. We do 500iu/day for the kids and 5000iu/day for the adults. I have had my levels tested and the sun wasn’t doing the job (tan skin) so I had to add the supps.
I do agree they should have had a couple more study dosages at least. There might be a plateau effect somewhere.
I think you can up your kids’ D3 a little, especially if they sometimes catch colds and other viruses.
NA is North African?
We homeschool too.