Big Basin Redwood State Beach/Oso del Oro (AKA Waddell Beach), is a long, exposed stretch of sand that gets pounded by wind. Great for wind/kite surfing, not so great for beach going with little kids. The wind really drives the sand everywhere- in your eyes, ears, sandwiches. Yum O!
If you want to see some good kite surfing action, this is your place, but if you are looking for a hangout spot for your kids to play in the sand, this is probably not ideal.
Big Basin makes a terrific weekend camping trip - it's far enough away from San Francisco for rest and relaxation but close enough to avoid long drives w/ unruly youngsters. Endless activities to amuse kids - whether it's a short nature walk around the campground finding banana slugs, crawling into Redwood "caves" or climbing a tree. The park offers a range of hikes to please toddlers and teenagers and sponsors activities, too. Make it an annual trip with other families!