We were at ChiTAG with a toy that kids can't get enough of.
We brought two 58-Piece Bilderhoos Play Sets, one painted set and one natural, for the kids to try hands-on building and climbing and taking apart and building again. And did they ever!
Parents having trouble dragging their kids away from the 'hoos is a joy to behold, at least, from the Boss Elf's perspective. Really, I do have sympathy for them (I raised three), but I also know what the remedy is! :)
Building it himself.