bottle cap pictures?

[stinkycretingrl.livejournal.com]

so this weekend i want to make my nieces resin-filled bottle cap pendant necklaces similar to this for x-mas. the problem is that they are 20, 17, 14 and 12, and i'm not. i think they think my taste is too "uncool" for them! does anyone have any suggestions for pictures to put into the bottle cap that might be considered "cool" by them? thanks!