Since I have been an Airport LEO, I have never seen anyone but the involved airline issue the gate passes. Of course that's just at my airport, but I would assume it would be the same for others. I do believe TSA is the authority when it comes to airline employees issuing gate passes when they are not supposed to.

I know Southwest allows to accompany (or pick up) minors for free. United charges $99 (according to their ticket agents and website).