Ds2 is 16 months, and in the last week or two has been drinking very little. Normally, he'll have about 100 ml (cows) milk with breakfast, water during the morning and with lunch, 150 ml milk in the afternoon, more water and with dinner, and 100 ml milk at bedtime. Now, that's gone down to maybe 50 ml milk at breakfast, 100 ml in the evening, and very little (maybe 50 ml altogether) water throughout the day. He's eating ok, doesn't have very wet nappies, but still pooing as normal. I've tried different tricks, like different cups/beakers, heating his milk, even tried going back to formula, or very dilute juice, but these all these just seem to work once, then back to not drinking. The only thing that send to work is other people's cups - if he sees another child drinking, he'll be right there trying to take the cup away from them. If I then buy him an identical cup, he isn't interested.
He has a lot of milk in with his breakfast cereal (& yoghurt, so I'm not worried about calcium intake), but there's no way that's enough for the day. What else can I do?