Are they going off on their own? You could give a scavenger hunt of things to photograph or buy. Just off the top of my head: pic on the magic carpet in Morocco, ask CM to write your name in Chinese characters, buy a piece of chocolate in France's gift shop (they're under $1), etc. I can give more ideas if that's the type of thing you're looking for.
Or are you just looking for ideas of things that might appeal to teens in general? I would think they'd love the gift shops, especially Japan. Even if they didn't want to color a Duffy/Agent P at the Kidcot stations, they could get CMs to write a note or their names in that country's language. There are interesting things to explore or treats to eat in every pavilion. The performers are fun to watch. Are they into character meets? There are several around the WS.