Both the school and the officer have problems headed their way (most likely in the form of a lawsuit).
I've got kids, and anytime I decide to go up to the school and get them, I can. As parents they are your children, not the schools. Why does the school think they can hold children if the parents are there requesting that they go with them??? Crazy...
The principal, or someone else higher up at the school than the desk clerk/secretary, should have seen what was happening and immediately went to get his kids for him. And then that would have been the end of it.