Paris to Murren

Paris-Murren looks like a 5-6 hour trip, so it's very doable. I'd get the TGV ticket in advance for the Paris-Basel leg since there may be a discount over same-day purchases. Get the HFC for your Swiss travels once you reach Basel.

You may want to look into the Swiss Pass over the HFC, depending on your itinerary and how intensively you plan to use the public transportation in Switzerland. Your youngest child can travel on your own SP provide a parent is with them, so no need to buy aseparate pass for him. I don't know if kids need their own HFC. I believe you have to buy the SP in advance before your trip.

Edit: The SP family card covers kids 15 and under.

This may look complicated with a lot of connections, but it is actually quite easy. The trains in Switzerland are well coordinated. It seems to me, it took us about six hours. Totally doable in a day -- in fact more like a half day.

Yes, the Swiss pass products kick in from Basel (the official border station) and train connections from that point don't need reservations, so just book the reserved TGV Paris-Basel.

The one-month Half-Fare Card for visitors also allows you to get the free Swiss Family Card for your youngest child, same as a Swiss Travel Pass does. However, the latter product offers a youth discount for the other teens, which the Half-Fare does not. You can see prices in chart format on our Rail Guide PDF or through SBB.

Pam,

Be sure to note which station you'll be using in Paris (there are about six).

"looks like it will be the Interlaken Ost - Lauterbrunnen - Murren"

That's the route you'll need to follow. However it's important to note that there are two routes you can take from Lauterbrunnen to Mürren, and it's important to specify which route you'll be using when you buy tickets. The two choices are.....

• Lauterbrunnen to Mürren via the BLM cable car and railway
• Lauterbrunnen to Mürren via the Post Bus and Schilthornbahn

Either method will get you there, but I'd probably use the BLM route.

Yes, it's doable in a day. There are numerous trains you could use but using an arbitrary date of 1 June, one of the quickest and easiest will be a departure from Gare de Lyon at 10:23, arriving Mürren at 16:28 (time 6H:05M, 4 changes). The choices may vary slightly depending on which day you're travelling. While 4 changes might sound onerous, it's actually very easy. This is the route you'll follow....

• Paris to Basel SBB via TGV (3H:33M). You'll have specific reserved seats on that train, so be sure to note the coach no. and seat no's. TGV travels at up to 300 km/h so that will get you there in the quickest time possible.
• Basel to Interlaken Ost (1H:57M). Note that there are two stations in Interlaken, and you'll disembark at the second one.
• Interlaken Ost to Lauterbrunnen (20M). For this segment you'll use the local Berner Oberlandbahn. Be sure to check the digital display on the side of the car to ensure that the car you're riding on terminates in Lauterbrunnen. Some trains split in Zweilütschinen, with the other half going to Grindelwald. Have your camera at hand as some of the scenery is beautiful.
• Lauterbrunnen to Grütschalp (4M). When you arrive in Lauterbrunnen, you'll see the cable car station across the street. Walk to the station, up the stairs and board the next cable car.
• Grütschalp to Mürren (14M). When you arrive at the top station, you'll see the small mountain railway waiting. Board the cars for the short ride to Mürren. You'll arrive at the opposite end of town from the Schilthornbahn, and depending on which hotel you're using, you may have a short walk. Exit the rail station either by going up the stairs to the main floor or just out the side to the street (I normally use the stairs).

Enjoy the Berner Oberland!

Thank you all for this help- will purchase TGV tix right away! We are excited!

You can purchase your TGV tickets either through the TGV site, which may forward you to en.voyages-sncf site. You can also purchase them through Trainline, https://www.trainline.eu, formally Captain Train, & they have an App as well. The cost is the same as through TGV. Both sites offer you the choice to select your seating, from Paris to Basel.
Enjoy your trip.