If you can sneak away for some golf, Encinitas Ranch is my favorite coastal North County course (Encinitas Ranch Golf Course - Encinitas Golf Course | JC Golf).

Others may argue, but the best carne asada burrito in the world can be found at Juanita's (Juanitas Taco Shop : Map & Driving Directions). None of the "let's-put-rice-and-beans-and-every-other-crap-we-can-find-in-the-tortilla-and-smother-it-with-sauce" nonsense. Just seasoned/grilled carne, cilantro, onions, and a little green sauce in one of the biggest damn tortillas I've ever seen. Stuffed full of goodness; making myself hungry now. The original location that's spawned lots of lesser (Roberto's) imitators; I've been going there since the 80's. Can be busy; often a large late-night crowd either pre- or post-imbibing.

Rather than the (spectacular) San Diego Zoo, spend a day and head east to the Zoo's Safariland Park (San Diego Zoo Safari Park). Just a little southeast of Escondido; a real treat. Park closes at sundown and can be pretty warm this time of year. At the end of the day, stop (as others have mentioned) for fine semi-upscale pub food and terrific craft brew at Stone Brewery just off I-15 in Escondido.

Another alternative if you want to drive back to the coast through Rancho Santa Fe is to have margaritas and Mexican at Hernandez's Hideaway overlooking Lake Hodges (https://plus.google.com/112259086888844992069/about?gl=us&hl=en). Food is okay -- hit and miss, really -- and depending on how busy it is the service can be spotty. But excellent margaritas and a nice view of the lake.

BTW, traffic on I-5 (both directions) between Camp Pendleton and La Jolla sucks on the weekend, no matter what time it is. If you're going north/south to San Diego, try 78 east to I-15 south; if your itinerary allows, catch the Coaster (train) in downtown Carlsbad; will take you all the way to the downtown SD where you can walk and/or take the trolley around the Gaslamp, Seaport Village, etc.

Hope you and your family enjoy your trip!

Just wanted to thank all of you for the great suggestions. We just got back a couple of days ago. Carlsbad was great as was San Diego. The kids enjoyed Legoland but my wallet did not! Old San Diego, La Jolla Beach kayaking-all a blast.
I saw an air cooled 911 cabriolet driving along the road along the beach. Maybe a pelican?
We sent a few days at the West Inn and Suites before going to Vancouver to visit family. Nice to be back home though.