A timed competition Obstacle course sounds like a fun idea. Use of a trampoline in there somewhere. A low balance beam over fake foam spikes (with possible swinging foam blades). Bagua lotus posts crossing (coffecans filled with cement placed in a dice's 5 pattern), Dive thru a fire hoop...etc.
Other ideas...
- Hire some local "Wushu" guys to do an acrobatics martial arts performance:
- Hire a Chinese Dragon team from a local Chinese martial arts school, to put on a show.
Rent an inflatable bounce tent. Kids love to jump.
Other event ideas...
- Pole stab accuracy test: Hang a small bell or tennis ball from a string. Standing from behind a line, they get a certain amount of attempts, and accuracy is logged. Either something like 3 for 3, or 10 of 10... or hold a competition that widles down.. or simply just do it for fun. Weight can be added to the pole front as an additional challenge.
- Jump Kick challenge: Using a trampoline, run, jump, then kick a foam ball or handheld paddle. Raise height as everyone passes it... Highest kick wins.
- Subzero Limbo slide: Using a slippery +1mm thick plastic sheet, like a slip-n-slide... wipe it with Formula 21 to make it super slick without need of water. With socks on, have them get a mild run start... and try to slide under a foam pool log thats on an adjustable height holder.
- Karate Champ Bonus round test: Using foam balls, launch them at a kid thats in a circle. He much not exit the circle. He can jump, duck or use a punch / kick to use against the attacks. Could also try this using a 4ft pole as the only means of defense.
- If you cant bring a full coinop in... (im pretty sure the dojo wouldnt mind it being in the school a few days prior... if its set to freeplay

) You can bring a console such as a Genesis or Snes. You can wrap it in a dressed cardboard box with controllers sticking out. I did this for a Halloween party at a Pizza Hut I was working at, in my youth. I had Ghouls and Ghost on a Genesis, and it was a huge hit.
- Try to make at least one game / event, a Teamwork event. Teamwork is important to help them realize the value of their friends... as well as to give them great memories. It also imparts that martial arts are for protection of loved ones, rather than the purely self related pumping of the ego. IE: Help rescue Liu Kang (or a fellow child), using teamwork.. before he gets lowered into a pit of acid.
Edit.. More stuff as I think:
- 4" thick foam board, and rubber coated throwing stars.
- Archery event, using small kids bow / toy bow