If you're in Long Beach, most of the beaches can be fairly quiet - it's not really great "beach" going because it's behind the breakwater. However, if you to the far east end of town on what's known as the "peninsula," then you'll have a quiet area with sand and more wave action because it's where the breakwater ends.
It's mostly residential and you can access the beach via a boardwalk that's essentially the sidewalk in front people's houses - it also depends a bit on whether the sand's been pushed up to make a berm for the storm season. I'm not sure if that's OK now since it's summer, but during the winter, I recall they did that as well as in Seal Beach