Parents, please be up to date with the current guidelines. The UK is unusual in Europe in a) having a quite poorly communicated Vitamin D (and calcium intake) policy and b) not having ANY monitoring programme to ‘enforce’ best practice.
So it is down to parents to be well informed.
For new mums, interested in making sure their babies are getting enough, this article by nutri.co.uk might be helpful (obviously, discuss with your GP before supplementing small babies just to keep them in the loop).
Update: low levels of magnesium (quite common in the affluent western world) make it hard for the body to use Vitamin D.
And for those of you who want to dig a bit more, this recent lecture by the famous geneticist Steve Jones should be interesting.