Hi Leah,
My husband and I were in the exact same position in October. We had a wonderful time at DL. We tried to focus on the rides that were unavailable at WDW, like Mr. Toad and the submarine.
However, we were also really impressed that the DL version of Haunted Mansion, Pirates and IASW were, in our opinion a little superior to their Florida versions.
As for other parts of So. Cal, I LOVE the brunch at San Diego's Hotel Del Coronado... there's a military base a few miles away, so you can see the planes flying from the beach, which your kids might love. And if you get a chance to see a show at La Jolla, it's well worth it.
In LA, if you can find a way into the Magic Castle, it's wonderful.