I am still nursing my 20 month old, but since I he was around 16 months old, my milk dried up due to pregnancy. I debated and debated whether to start an alternate milk source, but like pp mentioned, humans aren't really meant to drink other animal milk source, IMO. My son actually eats pretty well, so I'm not worried. What I do, though, just to put my mind at ease about the calcium issue is I steam very gently (brocolli, kale, spinach, beet greens, carrots, or whatever other veggies I have on hand), then I puree them in the food processor. I freeze the puree in ice cube trays, and add it to whatever I'm serving him that day i.e. rice, pasta, soup, etc. You can also grind up nuts and seeds (if they are not into eating them) and hide them in all kinds of things. It takes a little more effort (I know) than pouring a glass of milk, but I think in the long run they will be much better off with the variety. And who knows, they might even develop the tastes for those greens, nuts, and seeds as they mature.