my girl alwasy does not like milk. now she is 13m and changed to 2 milk + 2 rice per day.
she did not like water before. now she is drinking a lot. i think because it's summer and she exercises too much (walking for whole day). also, my maid usually will not use air conditioning in day time. that's why she feels thirsty (i think). so you can try to make your boy exercise more.