2 weeks in LA?

I would spend 2-3 nights at least in Las Vegas and 2-3 nights in San Diego, which is great for kids.

I assume that with 2 small children you won't be much for nightlife.

1 day to recover from traveling, lunch in Venice
1 day total for Beverly Hills, Hollywood, Mulholland Drive
1/2 day Downtown, including basketball game (Clippers tickets are less expensive than Lakers, and they have a more entertaining lineup)
1 day Malibu, Santa Monica, Getty Center (for the trip up and views)
your kids are probably too young for a studio tour or even Universal theme park.
1 day to explore - Griffith Observatory (If you miss the Getty), museums - recommend LACMA and Petersen automotive museum (across the street from each other). Or something else entirely.
Each of these is not even a full, packed day. You won't be able to do a full day with small kids.
Can't think of much else in LA proper except just exploring neighborhoods, shopping, eating - not easy with small kids

I would recommend 2 days at Disney - definitely not on a weekend or holiday. This will be the highlight for both kids. I would stay in Anaheim.

2-3 days in San Diego (drive) - the San Diego Zoo is spectacular. Could also consider the Wild Animal Safari or Legoland. Sea World would be my 4th choice. (Zoo membership is cheaper than 2 days admission, includes both zoo and safari). San Diego is also simply a much nicer environment for the ocean, although if you are from Sydney, I'm not sure this is much of a draw.

2-3 nights in Las Vegas - kids will detract from that experience, although still worth it. Don't drive there on a Friday afternoon/evening or drive back on a Sunday afternoon/evening.

I believe we are still only up to 12 days or so.