I would interpret structure to mean planned as in for a portion of the day things are set up in such a way that for sure the child is being active be it a game, a walk around the block, dancing to a video or whatever rather than just assuming because music was playing that they were active dancing.

Also since we deal with such a small number of kids we know which ones are active and which ones aren't and can plan accordingly as compared to as someone mentioned assuming the kids out for recess are getting more than just fresh air when they are still being sedentary instead.