We've done the drive from Richmond, B.C. to Anaheim and San Diego twice before on the I-5.
We have 2 young DDs. My DH and I like to take the "get the drive over with" approach.
NIGHT BEFORE THE LONG DRIVE (The after-work escape):
We cross the U.S. border and drive as far as Seattle. We stay overnight at one of the hotels south of Seattle, usually in the SEATAC area. We use Priceline to get a 3 star hotel for ~$27-40USD.
DAY ONE:
We get as far as Redding, CA, but make some pit stops along the way (usually at a Wal-mart or Target for bathroom and leg stretching breaks). It's usually 6pm when we arrive into Medford, Oregon, for dinner, and 10pm when we arrive in Redding. We stay at the Holiday Inn Express there (overlooks the hwy), which includes the breakfast in the AM so we can get back on the road quicker.
DAY TWO:
We go from Redding to Anaheim. We do the same with the pit stops, and usually get to Harbor Drive by around 7pm.
Our DDs are always cooperative on the drive...'cos they know where they're going
To make the trip even more economical, we book our Anaheim and San Diego hotels on Priceline. The best we've done? Hyatt Orange County for $26USD/night and the Hyatt La Jolla for $58USD/night.
Of course, you can split the drive into 3 days, which may make it easier. But my DH and I didn't want to spend our precious vacation time by extending the drive anymore than it was. Hope this helps you in some way!!!!