TLDR: Looking to plan a quick fam trip to California in late Dec/early January.  What's your suggestions for parks that won't be 3 feet under snow or mostly closed down?

Being from Texas, that white substance called snow is quite foreign to me. While I would love to see some, I don't ski or snowboard.  I also will have the wife and 18mo kiddo in tow, so primitive backcountry hiking/camping is out as well.  So basically day hikes, nice scenic views, etc.

Yosemite?
Joshua Tree?
Sequoia?

Any consideration to recent wildfires or will that be a moot point by late December?

A lot of the high elevation/Sierra parks close down during the winter. It's impossible to get up there anyway once the snow falls. They close off the roads. Even in late spring ~ May/June, there is still a good amount of ice on the roads. Slip and slide.

Desert areas are nice in the winter, warm days - cool nights. Death Valley, Glamis, Anza Borrego.

The Northern pacific coasts are not bad at all. Not too cold yet, we usually do our abalone diving around this time of year but this season was closed. There are lots of cool coastal areas and vineyards up there about San Fran.

I'm reacting to the "would love to see some" part of your post.  All the Parks are open and are glorious in winter.  They are less crowded, too, except for Yosemite Valley, which is always full.

In the winter, you have to decide whether you want to go to the east side of the Sierras or the west.  Interstate 80 is kept clear all winter long but is subject to closure during heavy snow falls.   From So Cal, it is always too far north to be practical.  Many/most of the other roads that cross the Sierras are closed for the winter.

The west side has Yosemite Valley.  That is a HUGE plus and it's perfect for families.  It has tons of family-friendly day hike trails that will be open (unless we get an unexpectedly massive snow season).  You can go ice skating there, too.  Book accommodations ASAP.  If you want to see snow and play in it (sledding, tubing and skiing), they have the Badger Pass ski area just south of the Valley.  You can learn to ski in a couple of hours if you take lessons at the resort.

Sequoia is great in winter.  The roads are kept open.  You can hike the trails around the BIG trees.  They rent snow shoes (anyone can snow shoe).  There are great sledding and tubing areas, too.

If you go to the eastern side, there's Mammoth Lakes.  You can go sledding, tubing and snowmobiling in Mammoth Lakes.  Ditto on ski lessons there.

Death Valley is on the eastern side of the Sierras, too, and winter is the preferred time to go there.

There are lots of nice places to stay at all of the above.  The hard part will be picking just one.

Don't worry about the recent fires.

I’ve been camping in Death Valley in March, the weather is perfect. 80s in the day, 40s at night.

As Joshua Tree is likely my favorite of the three, I'd suggest it.  On the plus side, the snakes are fewer, and the days are cooler.  The nights can get darned cold, and you have the chance of seeing a desert thunderstorm (very impressive ).

Wildfires?  We may not be done yet.  There are several things to think about.  End of December, early January is, as elsewhere, school vacation time - usually about two weeks. typically the weekend before Christmas to the weekend after New Years.  It's a high visitation and vacation time frame.  Absent a winter storm at the time, the weather is much better than most of the rest of the country.  Snow is generally only an issue in the high country.  winter closures will be in place for the parks and highways in the Sierras and north to/through the Cascades.  The west edge/coastal mountains typically don't have snow problems  (unless near Oregon border?? don't know.)  The big name National Parks, Mt. Lassen, Yosemite, Sequoia and Kings Canyon have some access in the winter.  Significant parts are typically closed once storms begin.  Which may be now, depending on how the current storm activity works out.  The remaining open areas can be quite beautiful and crowded.  Local lodging is likely already booked up to accommodate tourism and winter sports activities.

Likewise, you could expect crowded conditions in other snow areas, like the rest of the higher elevation parts of the Sierra and southern California mountain resort areas.  If planning to make day trips to or through high elevation or snow prone areas, even day trips, etc., keep an eye on weather conditions and be aware of chain requirements.  Yes, you noted you weren't really interested in snow but storms can catch folks unprepared.  Tejon and Cajon Passes into/out of the L.A. area on I-5 and I-15 are at about 4000 feet and can have snow problems, chain requirements and closures during storm periods.  Banning Pass between the L.A. Basin and Palm Springs typically doesn't close.  Some of the other mountain passes between L.A. and Las Vegas can have snow problems during storms.

Joshua Tree, Death Valley and Anza Borrego State Park (more to the south, east of the San Diego area) are popular and it's generally good weather for them.   Besides Joshua Tree, near Palm Spring is the Palm Springs Aerial Tramway.  A small fire near the base has it closed now but it's expected to re-ope soon.  It takes you from about 3,000 feet in a canyon near Palm Springs to a recreation area at 8,500 feet on Mount San Jacinto.  Usually snowy at the top when your planning to be here but an easy trip, can be great views, and generally not a driving problem.

Tourism in the L.A. and especially Pasadena area is dominated by the Tournament of Roses.  Parade and bowl game.  There are some other bowl games as well, in the San Diego and San Francisco Bay areas.  San Diego, L.A., Santa Barbara, Monterey and San Francisco areas are popular, and there are national forests and state parks and other rec areas which offer camping and hiking, etc.

The Death Valley NP idea is a good one since that is the best time of year outside of the flower season which tends to run late April to May.

Do keep in mind the area is largely remote even though the maps make it look otherwise. That means that you need to plan ahead as there are not many places to sleep.

Aside from several of the east west passes over the Sierras closing in the winter, the bigger north south routes are kept open. Yosemite can be a nice trip in winter if you visit the valley coming into the park from the west along 120. Again, plan hotels in advance.

The big roads to Mammoth and Lake Tahoe areas stay open and will quickly open after a storm since snow is their livelihood.

Those visits are very worthwhile and the Owens Valley is very scenic year round.

Other than the politics in the dense parts of the big cities, the rest of the place is beautiful.

Mt. Lassen Nat'l Park closes, oh well.  "Temporarily" closed to a snowstorm, but may stay closed according to the NPS website.  According to CalTrans nothing has officially closed, except the higher areas of Mammoth

MOUNTAIN PASS: ROUTE: 2018/19: 2017/18:

2016/17: 2015/16: 2014/15: 2013/14: 2012/13: 2011/12: 2010/11:
Ebbetts Pass

SR 4

11/30 - 5/4 11/30 - 6/30 11/24 - 5/13 12/12 - 4/17 12/9 - 4/18 12/17 - 4/25 1/25/12 - 5/11 11/22 - 6/7
Monitor Pass

SR 89

11/30 - 5/8 11/23 - 4/5   12/9 - 1/13 12/18 - 4/10 1/25/12 - 4/16 12/15 - 4/29
Lassen Loop

SR 89

11/13 - 5/29 12/1 - 7/26 12/2 - 6/14 11/19 - 5/4 1/7/14 - 5/19 11/29 - 6/6 11/23 - 6/1 11/8 - 7/18
Sonora Pass

SR 108

11/21 - 5/3 11/30 - 6/13 11/16 - 5/18 12/17 - 4/17 12/9 - 4/18 12/19 - 4/24 1/21/12 - 5/4 11/22 - 5/27
Tioga Pass

SR 120

11/29 - 5/21 12/1 - 6/29 12/9 - 5/18 12/19 - 5/4 12/12 - 5/2 12/19 - 5/11 1/25/12 - 5/7 12/15 - 6/18
June Lake Loop

SR 158

1/3 - 4/14

12/31 - 3/17

1/15/13 - 3/13   12/15 - 4/18
Mammoth Lakes SR 203 11/15 11/6 - 5/30 11/21 - 7/13 11/3 - 6/3   10/28 - 5/23 11/10 - 5/22 11/04 - 5/30 11/9 - 6/27
Lake Sabrina to Aspendell SR 168   12/4 - 4/13 11/23 - 4/24 1/9 - 4/15 12/22 - 4/15 11/25 - 4/15 1/15 - 4/15 11/22 - 4/16 12/15 - 4/29

Once the snow sets in, you can't get east to west over the Sierras between Walker Pass or Rte 58 (a little quicker) and Lake Tahoe.  Even those roads may close temporarily due to an on-going storm but they try to keep them open.

As noted winter in the Sierras and the National Parks is fantastic.,  But winter driving is a challenge if you have never done it.  Which could be the majority of the people driving to the parks.  US-395, the only artery east of the Sierras is usually open but can close temporarily between Bishop and the Carson Valley in Nevada. I-5 through the mountains between the junction of I-5 and US/CA-99 and I-5 and CA-126 can close due to storm conditions.  So if you are here and the roads are open, you can use them until the next storm sets in, so you need to pay attention to the weather news.

CA in the winter is a good time to visit in most areas as you don't have the massive family vacation influx to many areas.  Beaches are cold but can be pretty in the rougher weather.

Didn't cut and paste well.

http://www.dot.ca.gov/hq/roadinfo/clsdlst.htm  for Mountain Passes.

http://www.dot.ca.gov/cgi-bin/roads.cgi  for current and local conditions.

I only go to Yosemite in the winter to avoid the crowds. Call ahead, if the road is open, you will not regret it.

Yosemite is stunning year round.  Winter is no exception.