OK, did the circuit with the kids yesterday. Had to improvise on a couple of things, like thrusters, but everything went well.
Today we had our first meet. My kids all improved on their times (expected, the adreniline rush of a meet will boost times), but the real shock was my 7th grade boy taking first place and out distancing the next runner by 30 yards.
Now, I can't say the workout did that, but this is the type of programming we've been doing for the past two weeks to prepare. We run race distance once a week, do long distance once, and the rest of the time we train in circuits and use sprints. Seems to work well for now.