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

Bhouston's You Never Know What Happens When You Leave The...
I left my phone on video record and captured this. Hmmm

Ezang's My New Metal Robot With Voice Commands...
New Up date My metal robot, Ez-builder software, IO tiny with my new speaker, RGB more to come next week thanks

Rgordon's Project Magnus On Hold
I have decided to hold up on Project Magnus I have been working on this build for several years now and it looks like it...