Some places might depend on how old the kids are...
Here's a few 'economically viable' kid-friendly suggestions:
A good day adventure for nearly all ages is: Bike riding or roller blading from Santa Monica Pier to Venice Beach (about a mile or so). Venice Beach is where the famous Muscle Beach is. Venice has some colorful characters but gets a little rough at night. Santa Monica Pier also has had a bit of a reputation at night, too so for night time in the Santa Monica area - Check out 3rd Street Promenade.
3rd Street (3 blocks from the ocean/pier) is blocked off from motor vehicles and at night the stores stay open and street performers entertain until 11pm/midnight.
LaBrea Tar Pits may be interesting for an afternoon visit. You could easily do the tar pits with a trip to Hollywood. Stroll the Walk of Fame and find the stars of your favorite singers and movie stars. If your interested and have some money to pay: There is Ripley's Believe it or Not and the Wax Museum is right across the street.
Mann's Chinese Theatre (with the hand and footprints) is just a block and a half from Ripley's. If it's hot (or you have money to spend) you can buy tickets and actually see a movie, too.
A favorite of mine is the Hollywood Bowl. Some afternoons you can go in and hear the philharmonic (or other) practicing. If there's a show at night you can still get seats for $3 each. Those seats are waaayyy back up in the trees but still can hear so clearly.
The Getty Museum (by West LA) or the older Getty Villa on PCH in Malibu (or Pacific Palisades - these towns are right next to each other) is very nice but the kids may not be too interested. Probably depends on what the exhibit is.
I love Santa Barbara (my home is just 30miles south of there). [Reference Hortensia's Post] I think it's maybe 1.25 hours drive from Santa Clarita but beautiful nonetheless. There is a honey-tasting room on the way (east of fillmore) and SantaBarbara/Solvang area has wineries if that intersests any of you.
Zuma Beach is a very popular beach in Malubu - just north of Kanan Road.
Take Sunset all the way out to the coast @ Pacific Coast Highway (PCH) and right across the street is Gladstones for Fish. They also serve pasta and chicken and whatnot but the atmosphere is fun and the view is spectacular. You can walk on the sand before or after dinner.
If you are around during the weekend, I might even be able to meet up with you.
Now wouldn't THAT just be the highlight of your trip???
-Aude.
The kids may enjoy a surf lesson.