Hey, I live between Carlsbad and Anaheim!
You could stop in San Juan Capistrano -- there's a really cute little street if you park in the lot off Camino Capistrano and Verdugo. It's right by an old railway depot that they made into a restaurant (Sarducci's), and if you cross the tracks there's a cute little street to walk down with a petting zoo, a couple of restaurants, a teahouse, and a few cutesy shops.
And the San Juan Mission is right around the corner -- it's pretty cheap to get in (maybe $5?), and the gardens are really pretty. My 4yo loves going to SJC.
Here's a map that shows that parking lot:
http://www.capistranodepot.com/map.html