They are using tippy cups for other drinks they need water too so just start giving it to them.. Mine likes ice in it to make it taste really good.
I am going to get on my soap box here, juice is not empty calories. If it is then an apple is empty calories with a little tiny amount of fiber, a peach is empty calories. A serving of 100% juice is a serving of fruit, and if you don't believe me then refer to the food pyramid put out by the Government. Read the label, a serving of 100% juice is about 8 ounces per day. Two 1/2 cup servings.
Here is a link to a web site that has good information. Both about what juices are healthier and which are higher in sugar.
http://www.ext.nodak.edu/juice.htm