McNear's Beach County Park in San Rafael is probably the most kid-friendly beach north of Santa Cruz. The beach faces east on San Francisco Bay, and is sheltered from the strongest gusts of wind. You can bring a carload in for $8.00 during the summer. Here's what you get for your money: a narrow strip of sand, lots of grassy areas that include both sun and shade, a few volleyball and tennis courts, and during the summer, a swimming pool complete with changing rooms and a snack bar. The swimming pool is $4 per swimmer, although very tiny tots are free. Parents must go into pool with kids under 7.

 The waterline closest to the grassy picnic spots is lined with rocks, but if you walk farther from the entrance (north) you'll get to the sand. The waves aren't big (this isn't the ocean) and it doesn't drop off too steeply. However, as with any open-water beach, swimmers should use extreme caution at all times. Note that this is NOT a particularly welcoming spot for dogs; signs on the sand say NO DOGS, and there are not really any trails for a longer walk. 

A variety of picnic areas is available. Larger areas can be reserved through Marin County's website:

 The park also permits people to bring in portable grills, and even has special containers set out for the used charcoal. So, if you're there on a busy weekend, you can set up your picnic anywhere on the grass, even if all the picnic tables are taken. Or if you're really lazy, just buy a corn dog at the snack bar!