Back in the 1950's in Finland they used to give newborn babies around 2000iu/daily during the first year. When they stopped doing that, (when the rest of Europe decided 2000iu/d was the safe upper limit for adults therefore it must be too much for babies) the incidence of Type One Diabetes rocketed and now Finland has more Type One Diabetes than almost anywhere else.

So we know giving 2000iu daily to children under 12months results in an 80% lower incidence of Type One Diabetes over the next 30 yrs.

Dr Cannell suggests 1000iu daily for each 25lbs.

64000iu/daily should be the minimum any breastfeeding mother takes daily that is the amount that allows vitamin d to flow in her breast milk and is surely the amount that human DNA evolved to work best with.

I can think of no logical reason why children of any age should have a lower 25(OH)D than is optimum for adults.
Vitamin d is crucial for over 2000gene controlled actions in the brain alone vitamin D3 upregulated 128 proteins that operate different enzyme actions in the brain. The kind of 25(OH)D kids would natually apply acquire playing naked in the sunshine is evolutionary natural. The kind of level most kids have nowdays is totally unnatural.