In the UK, it's recommended that all kids up to age 5, I think it is, have a vitamin supplement that contains vitamin D. It's because we don't get enough sunshine here for our bodies to make it naturally and it's so important for healthy bone development. There has actually been a resurgence of cases of rickets in recent years because kids aren't getting enough naturally (in large part because kids spend less time outside and we use more sunscreen that in previous generations). So yes, they do recommend you keep them on a vitamin that contains vitamin D through early childhood. Not everyone does, but I personally like the added reassurance. My daughter is 3 now and has always been a good healthy eater, but since you can't get vitamin D really through food, it has to be added into our diets. We started her on a vitamin at 11 months and she still takes it now. You don't have to put it in their milk. I just give her hers on a spoon (or in a syringe when she was smaller) and she loves it because it takes nice. We use the Wellbaby ones.