Tar pits!
http://www.timeout.com/los-angeles/things-to-do/free-attractions-in-la-best-places-to-visit-for-free
YES!! The Tar Pits, George C Page Museum, will interest every age. We were just there a few months ago. Never get tired of it and our son loved going there when he was in grade school.
La Brea Tar Pits are great, but I think the kids want a beach.
This family is land-locked, I believe.