So much to see and so little time. LA is really spead out but here is what I would suggest. Take the 405 north from Costa Mesa to the 10 and head into Santa Monica and the 3rd street promenade area. Plenty to see and do there and many places to eat. A lot of celebs live and play there.
From Santa Monica I would drive up the Pacific Coast highway to Malibu (about 18 miles) and see the Pepperdine campus. Its an amazing school built on the top of a mountain with a phenomenal view of the Pacific. My guess is that the kids are going to want to go to school there when they see it.
Backtrack on the PCH to Topanga Canyon Blvd and follow it through Topanka State Park to the opposite side of the mountain to the 101 (Ventura Freeway). Follow the 101 back towards Hollywood and hang out on Hollywood Blvd where there are a lot of attractions and places to eat. There are also tour places on or near Hollywood Blvd.
Some advice and a must. Make sure you have a GPS device on your phone or in the car to find your way around the LA area.
https://www.santamonica.com/santa-monica-neighborhoods/downtown-santa-monica-third-street-promenade/