Swiss Family Pass and French trains

A partial answer:

(1) A single ticket for the French portion (bought 2-3 months in advance to get the best price) is ultimately likely to be cheaper that a pass just for one journey. The same applies for Chamonix - Lauterbrunnen, it is probably not the best option to buy a Swiss-wide pass, but it may be a good idea to buy a Chamonix - Lauterbrunnen ticket and a local pass for the Lauterbrunnen area.
You need to go to sbb.ch and sncf.com to cost the individual tickets, and then look up the cost of a local pass, before you make your final decision.

(2) Don't know - sorry.

(3) "Where exactly would the French portion of the train ticket start -- at the last train station in Switzerland or the first train station in France?"
Neither. What matters is the changeover point from SBB (Swiss railways) to SNCF ( French railways). That is not at the border, but wherever the two railway companies tracks join. There are two possible routes Switzerland - Paris, via Basel SBB station or Geneva Cointrin station. In both cases the join is in the railway station. The quickest route from Lauterbrunnen is probably via Basel. So your Swiss pass (or ticket) covers your Lauterbrunnen - Interlaken - Bern - Basel (not via Zürich, that is longer). You then need to buy an online ticket from SNCF (again 2-3 months in advance to get the cheap prices) from Basel SBB to Paris Gare de Lyon.

P.S. make sure you get a "print at home" ticket for Basel - Paris. There are NO facilities at Basel to pick up pre-ordered SNCF tickets from at ticket machine.

P.P.S. There is no price reduction buying SBB tickets in advance, you might as well buy on the day. SNCF has a totally different pricing policy and offers reductions for early booking on long distance trains.

How many are traveling and what are the ages of the children?

In Switzerland, you may benefit from some type of pass. Look into the Swiss Card at 199 chf per adult. That covers your train fare from the Swiss border (and I believe Chamonix Mont Blanc counts) to your Swiss destination, and your train fare from there to your exit point from Switzerland (in this case Basel SBB station). While at your Swiss destination, it gives you half fare on all the covered local transport including mountain railways and lifts. If your kids are under 16, they travel free if you get the free Family Card.
http://www.sbb.ch/en/leisure-holidays/holidays--short-breaks-in-switzerland/swisstravelsystem/swiss-card.html
The full fare ticket from Lauterbrunnen to Basel is 65.40 chf, and the Chamonix to Lauterbrunnen is a bit more. So, in essence, you are getting a Half Fare Card for about 45 chf.
Basel-Paris is by TGV-Lyria train and you can find the best price about 3 months in advance. www.capitainetrain.com is a good place to buy that and the Paris-Chamonix tickets as well. Same price as SNCF with less credit card hassles.
At Gare de Lyon, you just change to the RER A4 to Disneyland.

I have done three trips where I traveled from Paris to Lauterbrunnen. I bought advance purchase TGV tickets from Paris to Geneva - quite inexpensively. I recall validating my pass in the Geneva train station. Then I had my swiss rail pass for 4 days with the family pass for my kids, and trained to Lauterbrunnen and all over that area. I believe I also got some nice discounts on the trip to the Jungfraujoch and other high mountain lifts, and we took a boat as well - I think from Interlaken to Brienz, then bus to the Ballenburg open air museum. The museum was also free with the Swiss Pass - what a deal. At the time I did the math, and I still have that spreadsheet, that was my best deal.

I have had excellent luck getting open jaw fares that are as good or better than round trips, but it's too early to get a great deal on your flights yet anyway. You may find a better deal that lets you fly home from Geneva or Zurich. I flew into London and out of Munich twice, once into Stockholm and out of Munich - love Munich and its airport! This time we are flying into London and out of Paris about $100 per person cheaper than round trip London.

Our daughter will be 12 when we go. (2 adults one child)

What website did you use to get open-jaw tickets? I must have been looking at the wrong ones.

Thanks for all your feedback! It's very helpful.

"Open Jaw" is pretty easy. Go to the carrier website or a site like skyscanner and select "multi city" and you put in your home airport and destination, then the city to fly home from and your home city, and voila!!

It should be within $£€100 plus or minus from the price of round trip.

I usually book directly with whichever airline I am using, and I check lots of options that would be agreeable to me. I would usually be happy to fly home from any one of several cities, then depending on airfare, I may change up my itinerary. It helps to be flexible and I wouldn't consider buying tickets for next summer before the first of next year.

Hi Jimmy,

When you consider the cost of the train tickets from Switzerland back to Paris, plus the cost of an additional Paris hotel room, not to mention the travel time, flying open-jaws out of Zurich or Geneva might not be much more expensive. You can check sites such as Orbitz, Travelocity or Skyscanner for options and price it out to see which is most economical for you. Below are answers to your specific questions:

1) Buying advance-purchase, single tickets from Paris to Chamonix and Basel to Paris would be your best option. Rail Europe - www.raileurope.com sells advance-purchase French tickets for a good price, and you can print them at home before you go. The French Rail website - SNCF (http://en.voyages-sncf.com/en/) also sells some very cheap advance purchase tickets called "prems" fares, but they can be difficult to purchase ahead online with a U.S. credit card. See this webpage for some tips:
www.ricksteves.com/travel-tips/transportation/trains/france-rail-passes#ticket-tips
For Switzerland, getting Swiss Cards for you and your wife will qualify you for a free Swiss Family Card, where you 12-year old travels free in Switzerland with you. The Swiss Card gets you from any airport or border station to anyplace within Switzerland and out again, as long as you travel the quickest, most direct route. It will also give you a 50% discount on any additional trains, boats, buses or high-mountain lifts you do between the two round-trips. See this webpage for details and to order this pass:
www.ricksteves.com/travel-tips/transportation/trains/switzerland-rail-passes
2) You should be able to activate a Swiss Card or railpass at the train station in Chamonix beforehand.
3) Most trains from Lauterbrunnen to Paris switch trains in Basel. You can buy the Basel-Paris train ticket ahead (before leaving home). There are frequent trains from Lauterbrunnen to Basel (hourly, with a train change in Interlaken). Be sure to give yourself a little time in Basel to get from the Swiss side of the station to the French side, at least half an hour.

"Most trains from Lauterbrunnen to Paris switch trains in Basel" - what a confusing statement. There are NO trains direct from Lauterbrunnen to Paris. You get a train from Lauterbrunnen to Interlaken Ost, another train from Interlaken Ost to Basel SBB (you sometimes also need to change at Bern or Spiez) and another train from Basel SBB to Paris Gare-de Lyon.

"Be sure to give yourself a little time in Basel to get from the Swiss side of the station to the French side, at least half an hour" - not true. The TGV trains to Paris are in the SBB part of the station, not the SNCF part. They come from Zürich and change crews at Basel SBB. If the SBB web-site says it is a do-able connection, trust it.

Chris, thanks for the clarification regarding the trains to Paris leaving from the Swiss part of the Basel station rather than the French side, but I would still advise giving yourself more time than 5 or 10 min. to switch trains in Basel, especially if you unfamiliar with the station and if you have already purchased a Basel-Paris train ticket. Since there are direct trains from Interlaken to Basel hourly, I think it's better to be safe than sorry, as many of the advance-purchase French tickets are non-refundable or exchangeable.

Sorry if my statement regarding the Lauterbrunnen to Paris trains was confusing. You are correct that there are no direct trains from Lauterbrunnen to Paris. If traveling to Paris from Lauterbrunnen, you will need to travel through Basel, Geneve or Zurich. The quickest, most direct route (with the fewest train changes), is typically through Basel. You will change trains in Interlaken and Basel to get to Paris.