Closets airport to DL is SNA (Santa Ana/John Wayne/Orange County (they can't make up their mind what to call this airport)). Second closest is ONT (Ontario), Third closest and smallest is Long Beach (don't know it's letters, but I know this is the airport where Jet Blue flys through). Last is Los Angeles (LAX). LAX is probably about an hour away, with SNA being about 20 minutes or less with no traffic. Also SNA would be closest to San Diego (of the ones up by DL, there's other airports further south towards San Diego) if you'll be staying down their and going straight to the airport from san deigo. You can either rent a car or take a train to San Diego. On your way down to San diego is LegoLand. It's a lot of fun, especially for kids. It's geared for kids 3 through 10. Any younger and there's not much they can ride (I think most rides have at least a 36 inch height limit), and over ten or twelve probably wouldn't be too interested. It's a nice place for adults to visit, but don't know if I'd spend the money if I didn't go with kids.
San Diego has Sea World, zoo. The wild animal park is up closer to LegoLand. Near LegoLand is outlet stores, it's been a while since I've been there, don't remember what they have there.
Most things are spread out here, and renting a car is probably the easiest to do, not like WDW where you can spend all your time without ever leaving Disney Property.