I asked my facebook friends for suggestions and found some great beaches that are geared towards families. There's a bigger list on my blog post, but here are the top suggestions:
Mother's Beach in Newport: A quiet beach that's geared towards families with a playground and other activities nearby.
Baby's Beach in Dana Point, a quiet family beach with low waves and sand, a marina, a playground, the Ocean Institute, and has a kids swim area and boundary markers for the kiddos.
Hope that helps!