There is growing evidence that all children between age 6 months – 5 years should be given multivitamin supplements, along with a healthy nutritious balanced diet.
There is no harm in giving it to all children (and even adults due to our ‘not so healthy’ diet).
http://www.nhs.uk/Conditions/pregnancy-and-baby/Pages/vitamins-for-children.aspx
We see in our clinics, that many parents, specially Asians, give their children lot of milk. It fills the children’s little stomach and then they don’t want to eat anything else. Milk does not contain enough Iron and they become Iron deficient. It may manifest as tiredness etc. They can be constipated as they are not getting enough fibre from food.
There are many supplements available ‘over the counter’. Choose the one that contains some Iron and Vitamin D in it. It will not be ‘therapeutic’ but may have enough for daily requirement.
https://www.vitabiotics.com/shop/wellkid/liquid?gclid=CjwKEAjw2qzHBRChloWxgoXDpyASJAB01Io0Dn0fxsQi0iVbwxvQPJq3KtBmhFLH_U7kpAfBWFqjCxoCc4fw_wcB