Why not drive all the way?
Hi Skol,
You may not be aware, but there is much to see along the magnificent Pacific Coast Highway. It is a single lane each way, and quite slow going.... even if you don't pull off in the view points. But of course, you won't want to miss them. And then there is Hearst Castle, which may interest the children. To plan to drive from Monterey all the way into LA may be a little ambitious. And arriving in LA after dark is not something I would recommend. Maybe plan to stop somewhere between Cambria and Santa Barbara, and make it into LA on the next day.
If you are into theme parks, then maybe four days in LA could be justified. But I would suggest cutting down the time in the cities, and plan to drive from San Diego to the Grand Canyon, South Rim. It will be a long day, but you will never regret it. Stay the night in the park, if possible. It's cheaper than the flights you mention. Spend the next morning sightseeing, and if you leave not too long after lunch, you can make it into LV the same night. It is about a five hour drive to LV.
This will allow you to see the GCNP, which most helicopter and charter flights from LV do not cover. They fly over the West Rim, which is the Indian reservation. It is not part of the magnificent National Park. (Mind you, it is still a great flight, but it would be in ADDITION to, not instead of a visit to the National Park.)
Excursions during your stay in LV could be to Death Valley - a place like no other on earth, and a good day excursion from LV. Then there is also the Valley of Fire and other parks and attractions.
Best you get a good paper map, and lay out this route. See what there is, which places are along the route, or not far off it, that may interest you.
Enjoy the planning.
Lifey