Families love their beach vacations, and California offers the chance to combine beach time with theme park time in Anaheim (home to Disneyland and Universal Studios Hollywood.)
Meanwhile, northern California has some stunningly scenic beaches, but take note: the sea is too cold for more than a quick dip, even in summer-time! And a tip from About.com's California Travel Guide: the coast often gets 'June gloom' (even into July), when fog stays on the shore.
For those seeking a resort, the upscale Ritz-Carlton Half Moon Bay sits on scenic bluffs 40 minutes from San Francisco, and combines luxury with kid-friendliness and Ritz Kids Club.
On another note: about 100 miles north of The City, on the dramatic Sonoma-Mendocino coast, visitors can stay at Sea Ranch Lodge, or rent vacation homes.
South of San Francisco, Santa Cruz has 29 miles of beaches and a classic Boardwalk amusement park. Big Sur State Park has a stunning coast; visitors can camp or stay in cabins, motels, luxury hotels, or a luxury yurt. See Big Sur Lodgings at About's California for Visitors site.
Halfway between San Francisco and LA is this California beach town, with 1200-ft. Pismo Pier. Play on wide, sandy beaches; dig for Pismo clams; explore sand dunes or tide pools; try sea kayaking. State beaches, state parks, nature reserves in the area; Monarch Butterfly Grove. See comment about "June gloom" above: spring or fall are good months to visit and less crowded too.
Huntingdon Beach bills itself as "Surf City USA", and offers beach hotels, surfing lessons, and proximity to Disneyland. Huntington Beach is in Orange County; see Orange County Beach Hotels. Upscale Newport Beach is good for surfing, and has an amusement park and Christmas Boat Parade.
Meanwhile, just 20 miles south of the L.A. airport, the luxury Terranea Resort has a scenic setting in the Palos Verde Peninsula, miles of hiking trails, a 9-hole golf course, three pools including a family pool with waterslide, kids programs, and teen activities.
Finally, "thinking out of the box", an interesting option is the Santa Barbara Family Vacation Center: low-cost beach-side lodgings plus many activities, on a college campus during summer. Santa Barbara is just north of LA.