J.M.
I agree with everyone about the dental issues. This needs to be broken now. The sippy cup fairy is a great idea. We do this with Halloween candy. Put all the sippy cups on the front porch, tell him the sippy cup fairy will come and take them to all the other little kids who need them, in exchange, she will leave a small gift. At Halloween, we put all the excess candy in a bag on the porch and the Good Halloween witch comes and trades it for a small present too. My son thought this was a great idea. You could also tell him that he is so big he has gotten too big for the sippy cups and then switch to the character paper cups with water. Make something up about the water for only big boys, babies drink milk at bed, he's not a baby now. Maybe get him something new to be a soother, a stuffed animal, etc.. Good Luck.