As a mom, I agree it really gets overlooked since you are corralling the kids and being pulled in many different directions. Some times sippy cups and bottles are "comfort items" to the child, and the worse thing you can do it take it away.
At the same time, as a museum professional, I pick my battles. Most good sippy cups these days don't leak, and if it is stashed away in the stroller or pocket of a diaper bag, I am happy.
However, I will tell guides and docents to give parents a gentle reminder and tell parents- at the end of the days toddlers are unpredictable.
