Over the last few years we have been doing trips with my family (with kids of similar ages ) into Switzerland..Let me suggest on the basis of my experience ..and you may tweak/ alter to suit your specific requirements .
1. Presume your kids would like to see lots of snow and mountains like mine do . Suggest a 3/4 day halt at Interlaken or Grindelwald ..This will be a base for you to do Jungfraujoch (my kids enjoyed the actives there including the Zipline etc on the snow - all for SGD 45 per person) and Schilthorn (a very different experience and also comes free with your Swiss Travel Pass). Enroute to Schilthorn you could do the kid friendly trek from Murren to Gimmelwald (authentic Swiss Village) before you take the cable car down .
The other mountain trip suggested would be Matternorn ...for which the base would be Zermatt
2. Based in Interlaken you could spent some time on the lakes (Brienz) .
3. A day trip into the chocolate factory at Broc and the neighbouring Cheese factory can be done ..out of INterlakken
4. A big swiss city experience in Zurich with excursions in to the Rhine falls . Zurich also has lovely city walks in addition to the FIFA museum and a good zoo ...and a few historical buildings
5. You need to add in at lease or two of the scenic trains ...Glacier express ( Chur to Zermatt ), Bernina (Chur to Tirano/Lugano), Golden Pass (Luzern to Montreux).. Kids find the Glacier Express longer..and so you could do the Bernina and Golden Pass .
6. Spend some time in Lugano /Locarno to get a flavour of the Italian side of Switzerland . Similarly a place like Martigny /Montreux provides a flavour of the French cultural influence .
7. A day trip into Berne ..whiich has got a few attractions for the kids .
All put a broad suggestion for a 10 day tip would be
Day1 Head to Interlaken and establish it as a base for a week .. Kids typically do not want to relocate every 3 days
Day 1 - Interlaken - Brienz - - Interlaken
Day 2 - Interlaken - Grindelwald - Jungrauch - Interlaken
Day 3 - Golden Pass - to MOntreaux - Martigny - Interlaken
Day 4 - Interlaken - SChilthorn - Gimmelwald - Latterbrunen - Intelralken
Day 5 - interkaken - Choclate (Broc) / Cheese Factory - Interlaken
Day 6 - Interlaken - Luzern (Scenic route) - City Tour - Boat cruise
Day 7 - INterlaken - Zermatt - Matterhorn - Interlakken
Day 8 - Transfer to Zurich - City Tour - FIFA musuem (kids love it) . Cruise on Limmat
Day 9 - Zurich - Chur - Bernina Express - Tirano/ Lugano - Return
Day 10 - Zurich - Rhine Falls - Rhein am Stein - Zurich
Day 11 - Zurich - Sargans - Appenzil or Mainefield (Heididorf) - Zurich .
You may want to keep one travel free day in your 12day trip where you can leisurely stroll around Interlaken , while the kids paraglide .
This is a broad itinerary ...you can tweak it ...Switzerland is always enjoyable .....have a good journey