dont want to add to the overload but if in Santa monica you might , instead, walking, rent a bike, rollerblading Venice Beach. Bikes are rentable where SM ends and Venice begins. If on a weekend it can be quite the visual experience. There are breakfast places and bruncheries.
As suggested earlier Disney is always nice but at 12-13 i suspect your kids have done that.
If the kids are at all artsy you could try the Getty Museum where the 5 meets 101 . It is a high vantage spot with wrap around balconies. If a clear day you have a 180degree wrap of the pacific and into beverly hills. Actually they have a damn good cafeteria in there and those tables would be on the balconies for great lunch views. there are 7 buildings devoted to media arts and art museums
Not to be confused with the Getty on the PCH in malibu. Spectalar but it is roman, greek, egyptian, etruscan sculptures with a lot of this outdoors.
There is a ton of stuff but i would, if you have not seen, either the Paramount studio, or warner brothers studio tours. Much easier and more condensed than universal studios which is an all day event. This tour would be closer to three hours. Note you must absolutely reserve a spot, online, to hope to get in.
Aspeople have suggested Santa Monica you could not go wrong there. It is a really nice spot and you may want to find out what al the fuss for "" in and out butger "" is about.
I think maybe you might want to get a small taste of all of this and return for a week at another point.