D.M.
Hi D.! I'm a member of Mom's Club Huntington Beach chapter. They set up playgroups based on your childs age. It's nice because the infant group has moms going through the same things. And as the get older together, they play together in age-appropriate groups.
I'd suggest looking into a group while you are pregnant. Sometimes it can take awhile for agroup to firm up. Dont' be discouraged. The groups grow and fill up fast but as new one always starts up.
You can check out:
http://www.momsclub.org/links.html#California
or another good area to search is: http://www.meetup.com/
Good luck!!