You might want to try and mix up some basic tumbling or rolls with techniques.
You can start your class with a reqular warm up, what ever that might be. And them let the kids do some rolls. Once they're watrmed up with that, then you can set up two line and make it a bit of a race. They can start by doing their roll, standing up in to a fighting stance and then doing their technique. What ever the particular technique might be for their rank. Run through the line twice and the first team to complete the drill and sit down quietly first is the winner.