And I'm north of WhaHappened. Which puts me about an hour from Disneyland.
Bring a stroller. You can also rent one there if you decide the other child needs a separate one.
Prepare to spend lots and lots of money. Not sure what the current food policy is, but you might want to go to the grocery store and pack some snacks and drinks.
For what to do on Saturday, might depend on which airport you are flying out of. I think there are 3 within 30 minutes of Disney: LAX, John Wayne (SantaAna), and LongBeach.
-Aude.