I don’t know how long a vacation you’ll be taking, but if it’s not very long, I would suggest deciding on either Northern California or Southern California – otherwise you’ll be exhausted and you won’t really see any of it. California’s very big!

You’ll have to come to Northern California for redwoods – it’s too warm & dry for redwoods in SoCal. So here are some things to do in Northern California:

San Francisco:
San Francisco Zoo
Oakland Zoo (nearby Oakland)
Six Flags Discovery Kingdom (nearby Vallejo)
Great America (nearby Santa Clara)
Golden Gate Bridge, cable cars, Alcatraz Island, Coit Tower, Fisherman’s Wharf, Chinatown, North Beach

Big Sur:
Redwoods, beaches, hiking, camping, swimming
Monterey Aquarium (nearby Monterey)
Nearby Carmel (where Clint Eastwood was mayor)
Santa Cruz Boardwalk amusement park (nearby Santa Cruz)

Mendocino:
And parts north is where you’ll find more redwoods (& larger redwood forests)
Beaches, State Parks, Mendocino Headlands, lighthouses, whale watching, a Pygmy Forest

Yosemite National Park:
hiking, camping, the Ahwahnee Hotel, granite mountains to climb, skiing in the winter, waterfalls

For more things to see & do in Northern California see: http://www.discovernortherncalifornia.com

I hope this is helpful & that you and your family have a nice vacation, whatever you decide!

While I think the Redwoods and San Diego Zoo are excellent choices, they are on opposite ends of a very big state. I would say confine yourself to northern or southern depending on how long you’ll be there.

FYI, if you’re going to the San Diego Zoo, you also have Sea World down that direction. If you’re brave, keep going south and hit Tijuana, Mexico. It’s really "different." If you’re not going that far south, LA Zoo is a lot smaller, but still a zoo, and you’re near Griffith Park where you can hike, go horseback riding, and visit the observatory, and Universal Studios is nearby. If you’re into museums and more intellectual things, There is the Huntington Library in Pasadena with beautiful artwork and gardens. La Brea Discoveries is an interesting little spot in the Wilshire district with the tar pits and Page Museum. It’s small, but just standing there knowing saber-tooth cats and mammoths used to roam right where Wilshire Blvd. is interesting. Six Flags and Hurricane Harbor (water park) is just a bit further north from there. There’s always a bazillion tours past celebrity homes past and present.

If you’re going all the way up to the redwoods, which I highly recommend, might as well go to San Francisco and see the Golden Gate Bridge and visit Alcatraz. I’m not from the north, so I’m not as familiar with it, but it’s an old city and has neat historical sites and gardens.