From the second link Luddly provided: "The patrols will not be on the campuses, but rather in the area surrounding the schools. The idea is to have a visible law-enforcement presence around the schools."
I would be outraged if I were a parent of a child at one of those schools knowing that child molesters were surrounding schools looking for bad guys.
If a student at one of the schools I would feel betrayed by law enforcement.
As I know of no laws that restrict the movement of registered sex offenders (ones who have already done their time), except to be at schools, there really is no law against this. I once looked at the sex offender registry for my state, and they live all over. In fact, I bet I've run into them at a store and didn't even know it.
If I were a parent, I don't know how I'd feel about it. In light of the slaughter at Newtown, I probably would be OK with it.