2 nights-Locarno vs other options

One way to look at this is the travel time from Santa Margherita Ligure to each place you are considering. On SBB I see the following:

From SML to Locarno, 5 hours with one change at Milan; possibly less with an additional change

SML to Thun: this schedule appears strange, with morning departures taking 8-9 hours; mid-day 6 hours; later afternoon 5-6 hours ( so arriving 8 pm or later). Maybe someone can help explain this.

SML to Luzern: 6.5-7.5 hours, with a minimum of 2 changes at Milan and Arth-Goldau

Our inclination is to take the simplest journey (fewest changes) and keep the total travel time to 5 hours or less if possible. Those considerations both point to Locarno. The chance to see Valle Verzasca would seal the deal for me. We have not yet taken that step as we tend to travel in September, when the water in the river is meager (or so I have been told). In early July it should be fine.

But I will admit I am not a fan of Luzern; we have yet to find a hotel or a restaurant we like there. So for me, 2-3 hours there is enough.

Luzern's old town is cute but it is a quick visit, it is not that large. You could skip it altogether; Bern is a good substitute.
If you decide to skip Luzern, from Locarno to Mürren, I would suggest taking the Centovalli railway to Domodossola, then the train to Spiez (via Kandersteg), and on to Interlaken. It is a very scenic route.

Thank you all for your feedback!! I really appreciate you taking the time to look at the train routes/times, Lola. You are so helpful. :)
You've all helped me to confirm that Locarno is the way to go!

Balso, I didn't realize you could connect to Spiez via Kandersteg. I was looking into Kandersteg and Oeschinen Lake last night as a possible day trip from Murren. But if we traveled from Locarno on the Centovalli train, then up to Spiez via Kandersteg as you suggested, maybe we could stop there and take the gondola up and take a hike at the lake before continuing on. It looks like they have luggage storage at the Kandersteg train station. I saw on an old post on this forum though that there is danger of rock slides at Oeschinen Lake/Kandersteg due to melting permafrost/erosion. Does anyone know if it's still safe to hike up there?

I think we most likely will ride the Treno Gottardo to Luzern and then the Luzern Interlaken Express to Interlaken and on to Murren.
If we choose this route, is Oeschinen Lake/Kandersteg recommended as a day trip from Murren?

One more question: For this itinerary, is the Berner Oberland pass plus Half Fare Swiss Card the way to go? (2 nights Locarno, day trip to Val Verzasca, Treno Gottardo train ride to Luzern, train to Bernese Oberland, 6 nights Murren, 1 night Thun and one train ride to Zurich via Bern from Thun). Thank you!!

Regarding Oeschinensee, the community has the hazard zone under constant monitoring, and unsafe trails are closed. Here is a link to the January 24 2023 report:

https://www.gemeindekandersteg.ch/spitze-stei

You can run the report through a translator if you want to whole thing, but basically it says that the downhill movement of the slippage or landslide remains constant at 0.5 cm a day. Small spontaneous rockfalls or slippage can occur at any time, but they are expected tro stay with the permanent exclusion zone (marked Yellowe on the upper map and blue on the lower one).

You can see the open and closed trails on the lower map. You can also see that the “potential impact zone” (potenzieller wirkungsraum, the label for the blue area) comes right down to the lakeshore at one point, but dioes not extend to the Berghotel or other buildings there.

Is it safe to hike there? Yes, on the open trails. They are monitoring things very carefully. The question is whether it will make you nervous or uneasy, or lessen your enjoyment in other ways. Our favorite hike there is to the Fründenhütte above the lake, and that is within the closed zone, so we won’t be going there in the near future. We used to enjoy an overnight iat the inn by the lake, but they are closed in the hotel portion; only the restaurant is open for day visitors.

To answer your other question, an 8-day Berner Oberland Pass plus Half Fare Card would be my choice. Get a free Family Card for your son with one of the parent Half Fare Cards, and he will travel for free everywhere, even outside the BO pass validity area.

The BO Pass will fully cover your travel for. Luzern to Mürren, almost all lifts and boats during your time there (exceptions for the Schilthorn and Jungfraujoch train), travel to Thun after your 6 nights in Mürren, and train as far as Bern on your way to the airport (this would be day 8 on your pass).

If you do go up the Jungfrau, use your BO Passes for free transport as far as Eigergletscher station, and then the Half Fare Cards for 50% off beyond there. You must buy tickets for that portion before you board the train at Kleine Scheidegg or Eigergletscher.

If you choose to go the other way, via the Centovalli Railway and Domodossola, the BO Pass will cover all the way from Domodossola to Mürren, IF you take the regional train via Kandersteg. You must ensure that you board the correct train at Brig. you can see this on the validity map:

https://www.berneseoberlandpass.ch/assets/Uploads/BLS-BO-Pass-M-24-WEB-komprimiert_compressed.pdf

Lola, thank you so much for this extremely helpful information!! I really appreciate you sharing the map with the potential impact zone for landslides. Also, thank you so much for the recommendation on travel passes. You have made some of this trip planning much easier for me!! Thanks again, and happy travels to you. :)

I really enjoy doing this—-writing about Switzerland brings back lots of happy memories—-in this case, very recent ones, since we were just there in Mürrren, and then riding the Treno Gottardo, in September.