Anyways, the triangle works like this:
One sensei stands at each point at the triangle.
At the first point, the kids do a kizami-tsuki (lunging front punch) and basically try to score a standard kumite point.
Then they run to the next "vertex" where they work on their counter; the sensei will throw a punch and they have to block it and counter with their own attack.
Then they run to the last corner where the sensei is holding a kick back and they do 3 mawashi-geri (roundhouse kicks) in a row.
Then they complete the triangle by running back to the first sensei to start again.
Of course, this is all expandable in terms of having the sensei making it easier or harder for the students to hit them (especially at that first corner), adding more vertices (a Square of Death perhaps?), and/or spreading the corners out.
Aside from working a number of different skills, it also gets them moving and keeps the cardio up. And it's also a fair bit of work for the people at each point since they're dealing with a stream of people.
And it's fun! Which is a crucial aspect to training with kids =P....
Anyway, we're gearing up for a summer karate camp this July, M-F 3-5pm so if you're interested, make sure to get in touch.