We recently went on a GCA sponsored field trip to the High Museum of Art. We stayed about an hour and a half before the kids were ready to climb the walls. You are not allowed to take pictures inside, so just imagine the kids breezing through galleries of art. I think they did learn that there is a such thing as a painting and a sculpture. They asked if we could paint when we get home.
They also went to the "Toddler Thursday" workshop in the High Museum's basement and made their own sculptures with clay, pipe cleaners, and felt pieces. They are our dining room table centerpieces for now.