When we were there last week we were told that soda, milk, juice etc. were unlimited refills. However if you chose a milk shake or smoothie as your non-alcoholic beverage it was a one time drink with no free refills.
We were in WDW 8/19-8/26 on the free dining and were told at several places that milk was not refillable. Milk is the first choice of beverage for both of our sons 9 and 3. Soda and lemonade were refillable.