You’re right, by Thanksgiving the Sierra passes are usually closed. Last year was an exception, when the winter weather came so late and was so skimpy that Sonora and Tioga didn’t close until around Christmas and then reopened in May. Take it for granted that those will be closed, and if Thanksgiving comes and they are open, be thankful for the break—but because it means we’ll be in a drought, pray for snow and rain once you’re safely through!
For families with young kids, I think late fall is ideal for a first Death Valley visit. If you don’t know how they will react to a hot desert summer (125º or more), you can be more assured of a good experience if you go in milder weather. You can hike or just walk around more comfortably. You can wallow in the Sand Dunes or hike a gorgeous canyon like Mosaic without worrying about heatstroke (but don’t skimp on drinking water regardless of the season). I’ve found that most kids enjoy visitor programs that rangers give, and park staff make a special effort to involve kids. There are only limited programs in the summer; in July, you might see someone like me at Dante’s View or other visitor sites making informal contact with people, giving “mini-programs” or answering questions according to visitor needs, but almost no formal programs. From mid-October to April, you’ll see a variety of talks, guided walks, caravans, or longer hikes daily and some sort of activity each evening; schedules are posted around the park and on the website.
BTW, when you go to the Furnace Creek Visitor Center, be sure to ask about the Junior Ranger program.
Here are some details about the alternatives for getting to the park.
ALTERNATIVE 1: Hwy 50 via Tahoe is longer, but pretty. The most direct way is through South Lake Tahoe to NV Hwy 207, Kingsbury Grade. Westbound, it’s one of the most dramatic approaches to Lake Tahoe, and eastbound you’ll be able to get glimpses of the awesome views. But take care, and pull off the road if you want to stare; you’ll be mainly ascending, but the road is steep and curvy and can be icy in winter.
NV 207 goes to Hwy 395 near Gardnerville. You'll be on 395 for about 220 miles. The Eastern Sierra is a long string of wonderful places to stop and look around, go for a stroll, eat, take a picture, buy a memento (including some nice local arts and crafts), see a visitor center, park, or historic site; or stop overnight. You will never be more than an hour from gas, food, or lodging, even in winter. The towns with the most visitor services are Walker, Bridgeport, Lee Vining, June Lakes, Mammoth Lakes, Bishop, Big Pine, Independence and Lone Pine. The main visitor sites in winter are Mono Lake, Mammoth Lakes (Devil’s Postpile will probably be closed except to snowshoe or ski entry), Manzanar, the Alabama Hills, and Mt. Whitney. At Lone Pine, stock up on whatever you want (last real town before DV), then turn onto CA 136. From Lone Pine it is about 50 miles to Panamint Springs, 80 miles to Stovepipe Wells Village, and 100 miles to Furnace Creek; these are park resorts with all services.
ALTERNATIVE 2: Shorter and quicker, but far less dramatic. Get to Bakersfield (I much prefer 99 just because I-5 is so monotonous and it puts me to sleep, but this is your trip, not mine.). At Bakersfield, take CA 58 (Tehachapi Pass) or CA 178 (Kern River Canyon, Walker Pass). Neither is a bad choice, and the distances are similar, but 178 will take maybe 20-30 minutes longer. Hwy 58 is all freeway to the town of Mojave and is quite green, and you might see trains running along the Union Pacific mainline and the historic Tehachapi Curve. Hwy 178 is a twisty rural road along the Kern River and Lake Isabella, a manmade lake created by the damming of the Kern River for flood control. This is a popular water recreation area. If you take 58, take CA 14 north at Mojave, which will connect with 395; if you take 178, it will end at 395. Get to Ridgecrest, the last major town and shopping opp before DV, then go north to Trona. This is an interesting town, home to a major desert marsh mining operation with minerals harvested off the ancient Searles lakebed and processed in the refiners you’ll see. It’s also home to Trona Pinnacles, a huge expanse of tufa deposits left from when Searles Lake was much larger and deeper.
North of Trona is a signed junction for Death Valley via Panamint Valley or Wildrose-Emigrant. If you are OK with the possibility of some ice or snow, I suggest Wildrose, a mountain road that goes through a green, pretty area that surprises many DV newcomers. You’ll even see trees. A couple miles are unpaved gravel but OK for any car driven carefully. This road is narrow and twisty, with a 25’ vehicle length limit. The other choice, Panamint Valley, is also scenic, but more classic Mojave Desert landscapes similar to what you’ll see farther into the park. Wildrose Road drops you into the park farther east, closer to Stovepipe Wells, Furnace Creek, and most major sights. If you are staying at Panamint Springs resort, you need to take Panamint Valley Road.
Alternative 1, via Tahoe and 395, is about 525 miles to Stovepipe Wells. Alternative 2, via Bakersfield, Tehachapi or Kern River, and Trona, is about 50 miles shorter. Of course, those are approximate, since people’s travel styles vary and they make different stops or detours. You’ll have to decide, based on your time frame and how much you want a scenic route. Maybe take one way going and the other returning, perhaps taking the Sierra route first to avoid long snow delays on the return trip when you’re more pressed for time (but being aware of possible tule fog on the San Joaquin Valley return trip).