Yes, this is for So. Calif. residents only. Adults must show proof of residency and one child gets in free with each paid So. Calif adult ($33 per ticket for the adult.). The reason AP holders got free child comp tickets, is that they would not have "paid" for admission, so with the child comp tickets they could still get a child in free with them.
I believe this "deal" lasts until Sept. 9th (Sept 4th?).