Munich, Vienna, Salzburg, Neuschwanstein, then Paris with 2 adults and 2 kids, 8 & 5yo

Fly into Vienna and out of Paris or vice versa
Train Vienna to Salzburg
Train Salzburg to Munich
Munich to Neuschwanstein Castle
Fly or take the train whatever you prefer Munich to Paris

Thank you Jazz+Travels!

P. S. I forgot to mention that we are coming from Los Angeles.

I have no experience with the Oktoberfest, but it would be wise to check the hotel prices in Munich during that period.

yeah the whole world wants to go to this Oktoberfest

Oktoberfest ends Sunday Oct 7, so factor that in. If your reunion is in Vienna Oct 4, that may effect how you want to do this, like fly to Paris in late September, then head to Munich. There is a direct late afternoon train that takes 5 3/4 hours, and many with a single connection along the way in the same or less time. Considering the time required to get to either Paris airport, arriving a minimum 1 1/2 hours before the flight, flight time of 1 1/2 hours, then at least an hour to get luggage and ride the S-Bahn into Munich, it is about equal time wise and way more relaxing.

You could also consider the Canstatter Volksfest in Stuttgart that goes until October 14. Stuttgart is on the way from Munich to Paris.

Oktoberfest ends on Oct 7 thus year, so it may be best to start in Paris and end in Vienna. How many days will you need in Vienna for your reunion? Does your 2 weeks (14 nights) include your long flights to and from the US? If so, that only leaves you 12 days in Europe. That will partly determine how many days in each of your other cities. I'd recommend:
Fly into Paris. Stay for 4 nights
Train or fly to Munich. Stay 3 nights. Visit Neuschwenstein as a day trip.
Train to Salzburg. Stay 2 nights.
Train to Vienna. Stay 3 nights. Fly home from Vienna
Book your US- Europe flights with an open jaw (multicity) reservation.
If you have 14 nights actually in Europe, add a night each to Paris and Munich or Vienna.

My husband and I took a non stop high speed train from Munich to Paris. We loved it, the train was comfortable and it was great to see the countryside. While in Munich we took a day trip tour of the castle with Mike’s Bikes and we also took a day trip to Salzburg.

I lived in Augsburg, Germany, 50 miles west of Munich and did the Oktoberfest three times. Hotels in Augsburg were booked weeks ahead of time, as well as Munich and anyplace close to Munich.

You may already have a hotel booked, but if you haven't, you might not find one.

Also, the Oktoberfest tents are not the best places for small children. I loved the fest, but almost everyone is intoxicated. We went with a group of 35 people and one guy got on the wrong train and was on the train to Salzburg instead of Augsburg before discovered.

If you still want to do the fest, I suggest going early, not wait until the tents fill up. Of course, then you will miss the real fun.
You can take the train from Munich to Fussen and Salzburg (do you plan to see Berchtesgaden?), but consider a tour from Munich for the Neuschwanstein.

To do all you want in Munich, Salzburg, and Neuschwanstein (near Fussen), you will need a week. Vienna will add a couple more days. Paris you could spend a week easily. You can take an overnight train from Munich to Paris.

Traveling with children is a piece of cake compare to whinny adults. I have been traveling with mine since they were born.
I loved the bicycle tour of Salzburg (with the sound of music). It was not hard. I did it with my 2 years old.
You are right about the trains. It is a joy to use them. Just pack a picnic for the little one or use the dinning wagon.
If you can go earlier than your reunion (for Paris), the weather will be better.