2 week trip with kids 6 and 9

Hi! If I am reading your itinerary correctly, you have 2 nights in each location, which leaves only one full day of sightseeing. Packing up and moving locations will also eat up more time than you’d imagine. If it were me, I’d allot more time, especially in Lauterbrunnen. There’s a ton to do in that area and then you have more flexibility if you have a day or two of poor weather. I spent five days in Murren with my kids, and there was no shortage of things to do. Just my 2 cents!

First, you're rushing through the Berner Oberland, which is going to be a lot cooler than the sweltering cities in August . And there are some great playgrounds in Wengen and Murren. I would recommend slowing down, adding nights to Switzerland, especially in the mountains. You have a an entire array of Disney- esque rides with the gondolas, cogwheel trains, boats, luges, cable cars. The Cabrio cable car to Mt Stanserhorn ( Lucerne ) is open air! There are flat areas around the Swiss lakes for bike riding.
Paris is coming off the Olympics and starting the ParaOlympics, so I'd avoid that area.
Simplify by moving less, slowing down, and perhaps you'll feel less overwhelmed.
You do need to book lodging asap, especially family lodging, as post- covid, places fill up quickly.
Have a wonderful family trip.

Sounds like great fun! Below is Rick's recommendation:

https://www.ricksteves.com/europe/switzerland/itinerary
Switzerland Itinerary
by Rick Steves
So much to see, so little time. How to choose? To help you get started, I've listed my top picks for where to go in Switzerland, and my plan for your best two-week trip.
Depending on the length of your trip, and taking geographic proximity into account, here are my recommended priorities:
3 days: Lauterbrunnen Valley (Berner Oberland)
5 days, add: Luzern and Central Switzerland
7 days, add: Bern and Lake Geneva area, connecting with Golden Pass scenic rail journey
10 days, add: Zermatt and Appenzell, linking them with the Glacier Express train
14 days, add: Lugano and Upper Engadine, connecting with Bernina Express and Gotthard Panorama Express train rides

I would suggest you spend more time around Lauterbrunnen, or stay in one of the villages above (Wengen or Mürren). Get the Berner Oberland Pass + Half Fare Card for the adults for the length of your stay (4 or 6 days) and everyone can ride all the trains, boats, and lifts (with 2 exceptions*) for free. *Schilthorn and Jungfrau train are 50% off.

There is a fairly flat trail for biking from Lauterbrunnen downriver toward Interlaken, or you could ride up the valley to Stechelberg and over to Trummelbach Falls to see that wonder.

https://www.truemmelbachfaelle.ch/e/

We have taken our twin grandchildren to Switzerland twice, first when they were 6 and this past September when they were 11. Both times they (and their parents and grandparents) loved the beautiful playgrounds in the Berner Oberland. Especially this one above Mürren:
https://swissfamilyfun.com/allmendhubel-flower-park-playground/

And this one above Männlichen. You can combine it with the easy “hike” (really a walk) to Kleine Scheidegg, and a train ride back down to Wengen.

https://www.maennlichen.ch/en/summer/experiences/alpine-herdsmans-playground.html

The kids and their parents also loved the cheese-making farm tour at Murren:

https://muerren.swiss/en/map/detail/tour-of-the-schiltalp-alpine-cheese-dairy-7cf1b3c5-4519-47a3-be48-807198a5b6e6.html

Their favorite thing in Luzern was walking the walls and exploring the towers:

https://little-edition.com/2019/01/17/walking-the-walls-in-lucerne/

https://www.luzern.com/en/the-city/sights/top-sights/musegg-wall

And a boat cruise on the lake. We did not stay in Luzern, we stayed a boat ride away in Weggis, right on the lake at a hotel with swimming pool access, a dock for swimming in the lake, and sea kayaks available for guest use.

https://www.gotthard-weggis.ch/en/

It was a short walk to the cablecar for the ride up Rigi to Rigi Kaltbad. One can board the cogwheel train to the top of Rigi there. (However, I don’t think Rigi offers things like summer luge and rope park like Pilatus does).

Agreed, you’re rushing and not allowing enough time for travel/checking in/out + exploring + weather upsetting your plans. Pick 3 bases and explore from there. These activities aren’t day specific, but give you an idea of what’s possible in a day.

Day trips to Bern and Zurich from Luzern are quick and easy, so use Luzern as a base for those. I wouldn’t add in renting a car and doing Colmar for this trip, unless you’re going to remove the Montreux or Zermatt portion and replace it with Colmar. If so, just train from Wengen > Colmar and then when you’re done there, train to Luzern.

1 - Arrive in Zurich, train to the Berner Oberland (Wengen) for 5 Nights

2 - Wengen > Mannlichen (Great playground) > Walk to Kleine Scheidegg > optional Jungfraujoch or Walk up to foot bath play area at Fallbodensee > Return to Wengen or ride the Eiger Express down to Grindelwald before returning to Wengen
3 - Murren/Schilthorn/Allmendhubel (another great playground and restaurant area) + optional North Face hike counterclockwise from Allmendhubel or the shorter family flower walk up at Allmendhubel
4 - E-bike the Lauterbrunnen Valley (Rent bikes at Imboden in Lauterbrunnen) and stop at the various waterfalls
5 - Ballenberg open air museum + Lake Brienz Boat Ride (Giessbach Waterfall hike)
6 - Wengen > Zermatt or Montreux for 3 nights
7 - Zermatt (Gornergrat) or Montreux (Lake Promenade Walk + Chateau de Chillon + Boat Ride)
8 - Zermatt or Montreux (buffer day for above or additional activities like a boat ride to Yvoire from Montreux or Sunnega from Zermatt)
9 - Zermatt or Montreux > Luzern for 4 nights
10 - Luzern - Mt Pilatus
11 - Luzern (optional day trip to Bern or Zurich)
12 - Luzern (optional day trip to Bern or Zurich)
13 - Train Luzern to Zurich Airport to fly home

The Open Air Museum is in Ballenberg, on the way from Luzern to Lauterbrunnen. Weggis (or Vitznau) as suggested by Lola sounds good. I'd say 4 days there. Then 5-days in Muerren. Visit Bern and Thun as a day trips from there. Then 3 days in Montreux, with a visit to Chateau Chillon or Gruyeres. Fly home from Geneva.

I think with young children, keeping the lodging locations to a minimum is beneficial. 3 places in 2 weeks is ideal. Zurich is...meh?

It's been a long time since we've traveled with kids your kids age but I still recall taking them around Scotland when they were around 6 & 9. They definitely had low thresholds of boredom-- especially at art museums-- and they wanted to see it all. Traveling to the next place was 1/2 the fun and lingering longer or going on a slower pace didn't suit them.

From the same RS page linked above here is RS's recommendation (which may not fit you):
Day 1: Arrive Zürich Airport, head to Appenzell (sleep in Appenzell or on Ebenalp)
Day 2: All day for Appenzell and Ebenalp (sleep in Appenzell or on Ebenalp)
Day 3: Leave early for Luzern (sleep in Luzern)
Day 4: Luzern (sleep in Luzern)
Day 5: Boat, then train to Lugano along Gotthard Panorama Express route (sleep in Lugano)
Day 6: Bernina Express to Upper Engadine (sleep in Pontresina)
Day 7: Upper Engadine (Pontresina, St. Moritz, and Samedan; sleep in Pontresina)
Day 8: Take Glacier Express; if weather's good, head for Zermatt; if weather's bad, consider going straight to Lausanne (sleep in Zermatt)
Day 9: Zermatt and hikes, Matterhorn-view lifts (sleep in Zermatt)
Day 10: If weather's good, spend more time in Zermatt and go late to Lausanne; if weather's bad, leave early for Lausanne (sleep in Lausanne)
Day 11: Take the Golden Pass to the Lauterbrunnen Valley. If weather's good, go early; if weather's bad, linger in Lausanne/Lake Geneva area and leave late (sleep Gimmelwald or Mürren)
Day 12: All day for lifts and hikes in the Lauterbrunnen Valley (sleep in Gimmelwald or Mürren)
Day 13: More time in the Lauterbrunnen Valley (sleep in Gimmelwald or Mürren)
Day 14: Early to Bern, then on to Zürich (sleep in Zürich)
Day 15: More time in Zürich, or fly home
Notes
Zermatt isn't worth the trip in bad weather. If your reservations are flexible, consider skipping that leg and going straight to Lausanne (take the Glacier Express only to Brig, then change for Lausanne).
To connect Luzern and Lugano, follow the Gotthard Panorama Express route, but don't spend extra for the official tourist package-trip.

Thank you for the thoughts and tips! If anyone is willing to take another look, I made some changes. I wonder if I need to shift something so that we have time to walk the walls in Luzern. I don't know if we'll do much on day 1 after our long flight from the US. Maybe we could do that on the Transport Museum day, but it might be tough to keep my family from spending the entire day there!

1 - Arrive in Zurich, head to Luzern
2 - Luzern (transport museum)
3 - Luzern (boat, then cogwheel train to Mt. Pilatus)

4 - Lauterbrunnen (travel to Ballenberg, open-air museum, on to Lauterbrunnen)
5 - Lauterbrunnen (Schilthorn and scenic walks)
6 - Lauterbrunnen (Kleine Scheidegg hike)
7 - Lauterbrunnen (Ruine Weissenau castle ruins and St. Beatus caves by Interlaken)

8 - Lausanne (Golden Pass Interlaken to Montreux, walk in Lausanne)
9 - Lausanne (Chateau de Chillon, lakeside bike ride after lunch)

10 - Bern (travel to Bern, walking tour)
11 - Bern (day trip to Murten)

12 - Zurich (travel to Zurich, free afternoon)
13 - Fly home

Unless you have an early flight, you don't need to go to Zurich the night before. It's easy to get to the Zurich airport from Bern, for instance.
I'd still add a day to Lucerne and the Berner Oberland, and deduct a day from Bern. Just not sure Bern will be that interesting for kids. No one is ever ready to leave the BO, and remember it will be warm in the cities, even Swiss cities, will be in the 80's in the summer.
With the current airline chaos, you have no idea if you'll actually get in the first day without significant delays, which is why is nicer to have an extra day at the beginning. And check market day in Lucerne, I think it's Saturday. It's fun to buy your own breakfast of the freshest breads, cheeses, and yogurts from the vendors.
Which Swiss rail pass will you have? I ask because with the STP the boat and cogwheel train to Mt Rigi and Mt Stanserhorn are completely covered. ( Pilatus is 50% off.)
There's also the luge-type activity in Lucerne, I've forgotten the name.
Thanks for sharing your evolving itinerary, it's encouraging when folks actually take our advice and modify their original plans. I know it's a lot of work to develop travel plans for the whole family. You're doing a great job!
Keep in touch as you progress. Safe travels!

The “luge-type activity” at Luzern that Pat mentions is at Fräkigaudi, on the way down Pilatus on the Kriens side. I think that may be already in the plan, but as Pat points out Rigi would be free if you have Swiss Travel Passes.

https://www.pilatus.ch/en/discover/fraekigaudi-toboggan-run

You haven’t asked about passes yet—-do you have a plan? The 2 children will be free on everything—-trains, lifts, boats, etc.—-if the parents (or at least one parent) get either the Swiss Travel Pass or Half Fare Card. A number of museums are also covered with the STS, or at least discounted. Here is the list (you will see Ballenberg, Chateau du Chillon, and others):

https://www.myswitzerland.com/en-us/planning/transport-accommodation/tickets-public-transport/museums-included/

Speaking of Chateau du Chillon, why choose Lausanne over Montreux? The Golden Pass train from Interlaken will take you to Montreux, and it is much closer to the Chillon castle (as in walking distance, along the lake) than Lausanne.

I haven't thought too much about passes yet, but will soon. I was wondering about staying in Montreux, but the RS guidebook does not list any options at all, so I just haven't looked much yet. I thought we would do a bike ride from Ouchy by Lausanne mentioned in the guidebook, but maybe we could stay in Montreux and do a ride there.

I would stay in Montreux over Lausanne. Montreux is a smaller town and has great walkability. We took our son twice to Montreux and he loved the day trip to Gruyeres (cheese factory, cows in the fields, walled town with castle) and Broc (chocolate factory geared more for kids than the Lindt tour in Zurich).

HI, I think this is our final itinerary, as far as how many days where, so I can actually start booking places to stay. Please let me know if you see anything that doesn't make sense in terms of logistics, route, or time I've allocated. Thanks! :-)

1 - Arrive in Zurich, head to Luzern
2 - Luzern (transport museum)
3 - Luzern (boat, then cogwheel train to Mt. Pilatus or Rigi)

4 - Lauterbrunnen (travel to Ballenberg, open-air museum, on to Lauterbrunnen)
5 - Lauterbrunnen (Schilthorn lift, see Murren, Allmendhübel, Gimmelwald)
6 - Lauterbrunnen (Männlichen Panorama Trail to Kleine Scheidegg)
7 - Lauterbrunnen (Day trip to Thun and nearby castles)
8 - Lauterbrunnen (Walk or bike to see waterfalls including Trummelbach)
Also interested if we have time:
Schynige Platte Botanical Alpine Garden and alp horn concert
Grindelwald Glacier Gorge
Would these fit in some where? The Kleine Scheidegg and Trummelbach days might have space?

9 - Lausanne/Montreux (Golden Pass Interlaken to Montreux, take a walk by lake or to see Lausanne)
10 - Lausanne/Montreux (Chateau de Chillon, lakeside bike ride after lunch)

11 - Zurich (stop to look at Bern and try to tour the clock - my husband and daughter are especially into seeing how things work)
12 - Zurich (Lindt tour, etc. - my husband went to Zurich for a work trip once and wants to look around again)

13 - Fly home