I agree that if your visiting LA with kids, you will need a car. No way around it. In Hollywood, there is the Hollywood Walk of Fame, Graumin's Chinese Theatre and loads of tour buses that can take you on a tour of where all the celebrities live. California is a big state and you will need to drive to see it.
Family fun things to do:
Free Things to do in Hollywood:
Are you planning to visit Disneyland, California Adventure, Knotts Berry Farm, Wax Museum, etc.? Then I would suggest you stay close to these amusement parks. Many of these places are geared for families.
Get yourself a free visitor guide from here for California, they are a wealth of information.
If your going to navigate the freeways I suggest you get yourself some good maps or GPS.
If your going to navigate the freeways avoid the rush hours 3:00-7:00PM. Take a deep breath and be patient.
Las Vegas you probably can get away without a car unless your flying there. If you stay close to the Las Vegas strip, it is easily walkable. Loads of places to stay on or near the strip. http://www.vegas.com/resorts/
They are plenty of types of transportation available, such as Taxi's, public transit (buses) and many of the Resorts have services where they can pickup you up and drop you off at the Las Vegas Airport. http://www.vegas.com/transportation/
If you want to see Freemont Street then you will need a car or just take a taxi there. Pretty cool with all the free light shows and a zip line, but stay within the confines of the Freemont cover. http://www.vegas.com/attractions/off_the_strip/fremontstreet.html
Here is good site with loads of info for your las vegas visit.
Forget US 66 or US 50 (the "loneliest highway" in the US), US 395 may have some of the grandest sections of highway in the US traveling along the eastern wall of the incredible Sierra range. The scenery is world class. You can drive the section from Lone Pine to Bridgeport in the course of a day ... or it can take you a lifetime. See more tips in my Lone Pine, Independence, Bishop, Mammoth Lakes, Lee Vining and Bridgeport sections.
Sea World: www.seaworld.com
Universal Studios: www.universalstudios.com
Native American dancers are fascinating to watch and it is interesting to find out about all the different dances and their meanings.
If you have a chance, try to attend a pow wow.
Try and stay away from the tourist traps if you can. The major theme parks are usually overcrowded unless you are visiting here when most kids are in school. The beaches are nice, but not all of them are good for swimming or surfing. The coastline is beautiful, but so are the mountains and the deserts. I have lived in Southern California and the Bay Area, but really love the Central Valley. You are truly in the middle of everything - beaches, mountains, Napa Valley...you can't beat it. There is so much to do that it would take several trips to get a taste of it all.
A ride up the Coast Highway is a must. The roads get pretty winding but it is worth it. Southern California is great for the weather and beaches, but I find that there are TOO many people there.
The Central Valley offers a lot to do. Hiking, bike rides, wine tasting, you name it we have it. San Francisco is only an hour away and Tahoe is about 2 hours - well worth the drive. There are lots of campgrounds, lakes and of course, the Delta which connects us to The Pacific Ocean. You can rent houseboats and cruise along the Sacramento River and the Delta and get in some great fishing.