We only allow 2 glasses of juice per day and not at breakfast time. The rest of the time they get water. It seems to work ok because juice isn't a forbidden drink but they know that it's mainly sugar and not as healthy as water. The twins are only 3 so it's still hard to reason with them about healthy foods. I just give smaller amounts when they ask for it and they know they only get one cup of juice at a time. If they are still thirsty, they drink water.