Transportation options during Christmas season in Munich/Nuremberg/Berlin

Those are major cities, so doing the trip by car would be a bad idea. You don't want a car in a city, and driving will take a lot longer compared to a 300 km/h train.

You can travel from Munich to Nuremberg for 36 EUR for the whole family by using regional trains with the Bayern Ticket and it will include all public transportation for the day. No reservations, and travel anytime after 9 am weekdays, anytime weekends.

You can get from Nuremberg to Berlin in under 3 hours with the ICE Sprinter. Your best price is to buy a nonrefundable, train specific tickets now. I am seeing 160 EUR for the family in the week before Christmas. So once you have hotels nailed down, you will know your travel date and can buy confidently. Hint, make your departure station in Nuremberg the closest S-Bahn station to your hotel, and you arrival station the closest S-Bahn station to your hotel in Berlin. That way your ticket will include the local transportation to/from the main stations in Nuremberg and Berlin where you get the ICE trains. And get seat reservations at 9.80 EUR for the group as the trains are likely to be crowded and you will want to sit together.

I just did this but in reverse--Berlin-Nuremberg--Munich.

The trains are easy and fairly efficient. All three cities also have very efficient and easy to use public transit systems.

As you stated, only use the car for going outside the city and even then, check public transit first.

I assume you know the markets usually close the 23rd or the morning of the 24th?
Are you talking about the auto museums in Stuttgart, which has great Xmas markets , and is so close to Esslingen, which the kids would LUV!
Use trains only- often Xmas market parking is a hike, and in most towns, the trains come right into the city centers.
Have a magical time.

Of course, if you are Munich, you must mean the BMW Museum. Going to Stuttgart seems a bit out of the way for just a 1-week trip. You will be busy enough with Munich, Nuremberg and Berlin.

Y'all are awesome, thank you.

• For train passes, where should I purchase in advance online for all these cities? Eurail.com? Never navigated the system in Germany.
• When folks say Christmas markets close early on 24-25, is anything else open during those days, especially in Berlin? I only heard the city was mainly open.
  • Out of all the castles, which ones are a must-see in our short time?
  • Any fun family-friendly spots for kids and off the beaten path ideas, I welcome recommendations. We love food, arts, culture, architecture.

Christmas Market sites
https://www.berlin.de/en/christmas-markets/
https://www.christkindlesmarkt.de/en/
https://www.munich.travel/en/topics/markets-festivals/christmas-markets

Purchase rail ticket for Nuremberg to Berlin
https://int.bahn.de/en
If you have issues with using your credit card, you can buy at Trainline with a small commission.
https://www.thetrainline.com/en-us?gad_source=1&gclid=CjwKCAiAu9yqBhBmEiwAHTx5py2y2VYrb5safc3THaCRXDlcEleB9YtKwzkAE5NgU3V9OQIC9njSohoCuowQAvD_BwE

Purchase rail ticket for Munich to Nuremberg
https://int.bahn.de/en/buchung/katalog/REGIONALEANGEBOTE/REKLATD00001C201?dbkanal_007=teaserBlock_1-1_button_RegionaldayticketforBavaria
You can buy this out of a vending machine on your travel day

Travel in Munich, including from the airport into the city.
https://www.mvv-muenchen.de/en/index.html

Travel in Nuremberg
https://shop.vgn.de/index.php/standardProductSale

Travel in Berlin, including to the airport
https://www.bvg.de/en/connections

With a short time, visit the Imperial Castle in Nuremberg.
https://www.kaiserburg-nuernberg.de/englisch/castle/index.htm

For train passes, where should I purchase in advance online for all
these cities? Eurail.com? Never navigated the system in Germany.

The big question is if you should buy a pass, you'd have to do the maths and compare prices. From Munich to Nuremberg you can take a regional train which is covered by the Bayern ticket, or Deutschland ticket, but you can also take the high speed train which is faster.

When folks say Christmas markets close early on 24-25, is anything
else open during those days, especially in Berlin? I only heard the
city was mainly open.

Many markets close on the 22nd or 23rd. Few are open after the 24th. Expect more or less everything to be closed on the 24th, but on the 25th you can find some open museums.

Out of all the castles, which ones are a must-see in our short time?

It depends on what kind of castles you are looking for?

In the cities markets are open through the 23rd and into the 24th. You will have plenty to see and do in Berlin until the day of the 24th. Christmas Eve will be a ghost town unless you are at Christmas Eve services. There are outdoor sites, so you can see those. And of course you will want to pack for your morning flight. I don't think you will have too many problems with closures.

This Berlin Christmas Market is open on the 24th - 26th.
https://www.weihnachtsmarkt-berlin.de/welcome