I don't think it's such an issue for a 16 month old as they certainly don't need too much milk at that age. Most of their nutrition should be coming from food now and if he has cheese/yoghurt etc just don't give him milk if he doesn't want it. My daughter would only have a cup of milk at night before bed and even now some nights doesnt want it. She was breastfed to 12 months and never really loved cows milk so has her calcium in other ways.