Morro bay is about 130 miles away and is an affordable, kid friendly place, though it is so small I wouldn't recommend it beyond a weekend getaway as it would probably be rather boring after that. Some of the best things are feeding seals at the aquarium, the clam chowder at the flying dutchman, and the harrbor tour. Also when I was a kid I loved Morro Rock, just the mythology surrounding it and to a little kid it looks huge lol.

Santa Monica