If you haven't already found it, Hydroguy's thread, "A DLR Guide for WDW Vets," is a must read for you:
San Diego is a must do-in my opinion if you have never been there. The beaches are beautiful, and your 6-yr-old would probably love Sea World and
Legoland as well, depending on his/her interests.
I think you have the right idea in sandwiching San Diego and maybe some sights around LA between a couple 2-day stints at DLR. This would let you start and end your trip with a little extra magic.