i've not used them for my son but here's what the US says
October 13, 2008
Doubling of Vitamin D for Children Is Urged
By THE ASSOCIATED PRESS
CHICAGO (AP) ? The country?s leading group of pediatricians is recommending that children receive double the usually suggested amount of vitamin D because of evidence that it might help prevent serious diseases.
To meet the new recommendation of 400 units daily, millions of children will need to take vitamin D supplements each day, the American Academy of Pediatrics said. That includes breast-fed infants ? even those who get some formula ? and many teenagers who drink little or no milk.
Baby formula contains vitamin D, so infants fed only formula generally do not need supplements. However, the academy recommends breast-feeding for at least the first year of life, and breast milk is sometimes deficient.
Most commercially available milk is fortified with vitamin D, but most children do not drink enough of it ? four cups daily would be needed ? to meet the new requirement, said Dr. Frank Greer, who helped write the report.
The new advice is based on mounting research about potential benefits from vitamin D besides keeping bones strong, including suggestions that it might reduce the risk for cancer, diabetes and heart disease. But the evidence is not conclusive, and there is no consensus on how much of the vitamin would be needed for disease prevention.