An awesome idea would be a fighting robot. Sure, they probably have one, but not one that destroys the other. So they can listen to you if you say "punch" or "kick" and they will do that. Maybe parts could fall off so that they know who wins. Kids would go crazy for that.
Other robots from Synthiam community

Luis's Using The Sure Dc Ss503v100 With Ezb4 From Ez-Robots
Using the Sure DC SS503V100 with EZB4 from EZ-Robots Using UART Communication We will be using these pins on the Sure...

Andy's Walmart R2d2
Hello to All, Here is the Walmart R2D2 project. I disassembled the unit and was surprised to find it was more than a...

DJ's Six Hexapod Robot Tracking Ball
This was a fun use of ARC to configure a Six Hexapod to track and chase a red ball. Earlier this evening, we had a group...