My Death Valley suggestion (valid for either 2017 or 2018 :D) is Darwin Falls. It’s a short side trip on a rough but usually okay for cars dirt road* to a spot unlike any you’ll see in the valley proper.
*always check road conditions before going off-pavement in the desert!
There are A LOT of options in the areas you are considering, plus all the additional suggestions. Probably the hardest thing you are going to have to do is realize you are not going to be able to see everything and prioritize accordingly. San Diego is great, Big Sur is great, Yosemite is great, Bryce Canyon is great, etc., but you will just not have time to do it all.
Last year we spent two weeks driving from the CA central coast (where we live) up to to Vancouver and back, and the year before we spent 3 weeks driving cross-country from the CA central coast to Connecticut. My kids were 10 and 12 during last year’s trip. So I have some experience with this. 
I think your general itinerary sounds fine. My general recommendation is to spend at least 3 days (2 nights) in any major location (Yosemite, Sequoia, LA, SF, etc.). You may have to cut back on the number of sights you see, but I have never regretted spending too long in any one place and I have a bunch of regrets of not spending enough time in places.
Make sure you map out how long it will take you to drive from location to location. California is HUGE, plus traffic can be brutal in and around the big cities.
Weather should be pretty good that time of year. I would book at least some things earlyish as others will also be going on spring break trips. Especially lodging around high-demand/low-availability places like Yosemite and Zion. Big cities are not as much of an issue.
It will be a great trip!
I’d swap out Six Flags Magic Mountain for Disneyland. SFMM is kind of a dump. Unless coasters are a top priority. Then SFMM is a better bet.
It is certainly an embarrassment of riches in that neck of the woods and the constant pressure will be no. of things seen vs time spent at each destination.
Many thanks for the suggestions so far, I’m certainly thinking of doing a circular drive around Zion, Bryce Canyon, then down to the south rim of the Grand Canyon.
Well we aren’t really sold on Disney generally and our kids absolutely love rollercoasters but…I’m wondering whether we should focus far more on the natural wonders and give them the time they deserve. If we happen to pass by a theme park and time allows then perhaps we can drop by (especially if the weather doesn’t play ball).
Assuming you’re coming from the UK to the US, may I suggest flying into SLC rather than LAX or SFO? Not only might it be cheaper, you can bookend the trip w/ Utah’s parks. No rushing on the first 2-3 days of jet lag b/c you’re at your own pace, then south west to LA or north west to Reno and Northern CA. There will still be snow on the higher elevations as well, even in April. Thanks to AirBNB there are quite a few more affordable overnight options near the parks in Utah than there were just 5 years ago.
So, you’re planning a trip to the Mountain West, not the West Coast?
Or maybe Knotts Berry Farm…
I know SFMM was nasty in the 90s; there was so much gang activity that the security people were uniformed and armed. That’s kind of off-putting. Has it gotten better? (It’s hard to imagine it could get worse and still stay in business.)
Two of the oldest wooden roller coasters in the US are in California–one at the Beach Boardwalk in Santa Cruz and the other at Belmont Park in San Diego. They may be tame by modern standard but they’re still extremely fun to ride.
Sounds like a fun plan. One unique thing that tourists like to do in L.A. is to get tickets to watch one of their favorite shows being filmed. That would take up a full day though as there is lots of sitting and waiting involved.
If I had to choose between Knotts, SFMM or Disneyland, it would be Disney by several miles provided you can go on a weekday when the local schools are in session. The experience is unlike any other amusement park in the world. You can probably use isitpacked[.com] to get an idea of when the good days are.
And also echoing that the 99 is fine now. I drive it frequently and most of it has been upgraded to three lanes each way. There’s a good airplane museum just north of Fresno if you like that stuff.
Knotts, Disney, Six Flags, in that order.
Glad to hear the 99 has been upgraded…finally. I still wouldn’t drive it if I could help it. The coast road is gorgeous, if slow, and you can hit the aquarium that way.
As people have been noting, be prepared to be flexible with your plans if the mountains have gotten a bunch of late snow. That will close Yosemite and the passes. In that case you could fly into LA, drive up through Death Valley, then loop down to Vegas. Hit the Grand Canyon, then take the 15 south to San Diego. A couple of days there, up to Knotts/Disneyland, catch a baseball game, then up the coast, hitting the aquarium on your way to SF. Pick up Sequoia on the way if you wish.
I think this is a very important piece of advice. You could spend all of your time driving, getting out of the car to look at something, and getting back in the car. Spend more days at fewer places if you want to really get to know some of the regions you’re going to visit. For example, I couldn’t imagine spending less than three days visiting Yosemite or all you’ll do is get driven around the Valley and see everything from a tram.
My suggestion is, unless you are having a conversation in Los Angeles, to eschew the “the” in front of highway numbers. I’ve never heard anyone say that unless they were from L.A., and only particular freeways, like I-5 which they call “The Five”. People up this way may use “the” in front of named freeways, like “the Bayshore” instead of 101. But that’s it.
Also: the ocean is only warm south of Santa Barbara. North of there it’s as cold as the North Sea.
Also: many people from Europe have a hard time grasping how different distances are here. Being that they are much much much farther. California alone is almost 1300 kilometers in length. Driving from San Francisco to Los Angeles will take you 8 hours – although several hours less if you drive down “the Five” which is very boring and featureless. So, a common suggestion is to plan to just visit one part of the state, or a couple of places only a few hours away from each other. Like Death Valley and Disneyland, or Big Sur and San Francisco.
Another feature of California is that the urban areas are very congested and can be quite difficult to move around in, because public transportation, with the sole exception of the urban core of San Francisco, is very undeveloped. It behooves travelers to plan for this, for example booking a hotel as near to the venue you want to visit as possible.
full disclosure: I’m a native Californian and have come to hate the place. Well, not the place itself, just the 40 million people I have to shove aside just to draw breath.
Also something rarely mentioned in tourist brochures is how much nothing there is between things. Case in point being Nevada, an enormous desert between the Sierras and Utah, which itself is mostly an enormous desert. Don’t underestimate how long and boring a drive you will be in for to get across it. This is a couple of days of nothing but driving across a featureless windswept virtually lifeless landscape with nasty little trucker towns hours apart. If you have limited time and have to see Zion, fly there.
Winnemucaboth resents and represents this sentiment. When you’re excited to see Reno (and its satellite of the Bowling Museum and Hall of Fame) you have seen true desert driving. But! For folks who don’t often see such wide, open spaces (that aren’t ocean) it might be interesting enough once or twice.
“The” belongs in front of every freeway number. Anybody who eschews this convention is a furriner, or worse yet, a Sanfransican!
This has not been the case for 20+ years.
You’ll be behind semi trailers for hundreds of miles though.
Funny, I was thinking of Winnemucca when I wrote my comment. Weird, huh?
I beg to differ. I did the 99 a few years back. Even with freeway sections I ended up behind agricultural equipment more than I wanted to. Now that it’s 3 lanes and restricted access all the way, that might be different. But there’s a reason I take the 5, boring as it may be, and the lack of Bakersfield isn’t it. 