I wonder what they consider a toddler? Feb 4th my husband and I were on an early morning (6:40am) flight from DFW to MCO on American Airlines with our very tiny 3 y/o GS. (He is actually so small that most people think he might be barely 2 y/o.) Our grandson is never without his sippy cup and we thought that as a toddler obviously drinking his apple juice from the cup, that he'd be allowed through security with it. Nope! The TSA agents said he had to dump it. We had a very irritated, sleepy 3y/ol: snip
My guess is that if you had the juice in a bottle instead of a sippy it would have been allowed. You are right though the exemptons on liquids for babies and toddlers is subject to interpertation on a few points. Age is one and necessary for the flight is another.
For children over say 2 - the best thing to do is bring foods and snacks that arn't liquid, bring the sippie cup empty and purchase milk/water/juice after security.