Switzerland, 8 Nights with Two Children, September or October

I would say September is better than October. The weather starts to turn in the second half of September. It varies from year to year, but the later you are the more risk of cloud and rain.
And some places close for end-of-season after September.
And the days are shorter in October.

For accommodation and general info about Grindelwald, see here: https://grindelwald.swiss/en/summer/

Thank you for the information about the weather and accommodations.

In your opinion, do you like the tentative itinerary. I wanted to limit the number of bases with small children. Do these places have activities, parks, farms, etc. for children? I am open to other place suggestions too.

Thanks again.

Mike, it sounds like a good itinerary, for young and old.

Luzern has an old town, a lake with boats on it (a big lake, it takes the boats hours to reach the far end), and views of mountains. For two days, I would say one day looking around the town, and one day on a boat. You can go out on a boat, and back by train. The town centre is pedestrianised, so toddlers don't have to have their hands held all the time, they can toddle along after you.
Some photos here: https://www.schweizfotos.ch/luzern/stadt-luzern/
and here: http://www.schweiz-foto.ch/Luzern/Luzern/Bilder.php
Plus a 360° panorama here: http://tour.luzern.com/360/en/

Grindelwald is in the mountains. It is totally overwhelmed by mountains.
See this photo: https://cdn.content.tuigroup.com/adamtui/2017_7/13_8/733bf1a4-6ac6-4d9b-9133-a7af008b5381/SWI_GRI_F0210WebOriginalCompressed.jpg
You can see the railway station in the bottom left of the photo, so even the town centre is near green.
The chief activity is going up the mountains by the many railways and cable cars. This gives access to many places where you can gape at the mountains and the kids can just let off energy.
As well as cable cars and trains, I found this website from a local bus company which might give you some ideas: https://www.grindelwaldbus.ch/en

These are great links, pictures, etc.... Thank you so much!
Would you recommend staying in Zurich to be near airport on our last day? We could tweak and / or reorder itinerary if necessary. Having only two bases actually may be easier too if train to / from Zurich Airport is not too far away from Lucerne and / or Grindewald.

From Lucerne, Grindewalk, and / or Zurich can you take full or half day trips to any of the following places: Jungfrau Region, Zermatt, Geneva, Interlaken, Basel, and / or Bern? Would any of these places be worth visiting with our children?

Thank you again.

Good itinerary, not too rushed. I would stay in Muerren as it is more charming than Grindlewald and the views of the mountain, no car traffic environment are ideal. There are recreational opportunities for children. It is smack-dab across from the Jungfrau and you can perhaps take a trip to the Schilthorn, drop into the valley to see the waterfalls, etc. in Interlaken you can take a scenic boat ride, but I would not day trip to Basel, Geneva or Bern. Just enjoy Luzern and then the Jungfrau Region from Muerren. Your 3 year old will love the trains and lifts.

You’ll have the check train timetables at www.sbb.ch/en to see if you can travel to Zurich the same day as your flight. I think that is more easily done from Luzern so maybe you could go to Muerren (or Grindlewald) first.

Forgot to say, we have had good weather both months. We’ll be back there in late Sept. this year, in fact. You’ll need layers as you may need a tee shirt plus sweater plus jacket in the morning but be eating outdoors in shirtsleeves by lunch. Water resistant jackets are a good idea, sturdy shoes too.

Wow, thank you for this very valuable information. With this itinerary, would it be possible to stay in only these two places? It would make it much easier to have only two bases for packing and unpacking with little kids. If we need to be close to the Zurich airport, we could do that too if necessary.
Thank you again so much.

You can easily reach Zurich airport from Luzern; the train takes just over an hour for the direct train; a bit longer if you change at the main station. The train goes right into the airport.

If you have an afternoon flight, you can start from Grindelwald; the train takes just under 3 hours, most with 2 changes on the way.

That sounds great then to have only 2 bases. So maybe we will train the trip from Zurich Airport to Murren or Grindelwald. Then, our last base will be Lucerne.
Thank you