We do the same thing as Kate only now the 2yr gets juice. She still requires her sippy cup in her bed but it doesn't have to be milk anymore.
Unfortunately the issue with anything but water is that the sugars sit in their mouth all night and it's so bad for their teeth. I have a hard enough time brushing their teeth period that is one additional battle I don't need. Another helpful thing might be to switch drinking cups. New drink new cup. The 2yr gets the munchkin 360 training cup the 4yr uses oisiz water bottle but he had to be taught to all was close it. Our biggest battle is finding something that won't leak in their bed
It could be 2yr sleep regression. If you haven't gone fully cols turkey with the milk I would start decreasing milk quantity and filling with water. I'd younhad been giving 4 oz milk give 3oz mixed 1 oz and keep decrease over time. Till it's all water. If you've gone full cols turkey already i would stick to it. It will get better. We alway give our kids water in their beds but thats up to you