There are 6 special "display" cheese factories in Switzerland. With your plans I'd say Engelberg or Emmental would be the most convenient. As for chocolate factories your choices are even bigger.
Another kid friendly attraction would be one of the water fun parks (many also have sections for those seeking more relaxation than fun). I've personally been to and enjoyed the Alpamare on lake Zürich, the Engadin Bad in Scoul and the Säntispark in St. Gallen.
In February you should also have the chance to do some sledding/toboganning! The link is in German because the map is broken in English. But if you narrow it down and look at the idividual entries you can still switch back to English on the top where it says "Sprache v".
Since you'll be at the Zürich zoo in Winter I'd recommend (also) seeing the Masoala rainforest Hall in case you missed it.
Depending on how technically interested your group is you could visit the Technorama near Zürich or the Swiss Transport Museum in Lucerne. Lucerne is also worth a visit for the Chapel bridge, and the youngens should have fun at the mirror maze in the glacier garden.
As for your base. That depends on how much you're willing to travel on day trips vs staying at multiple places. You can probably fit all these things into a triangle between Zürich, Berne and the Jungfrau. Assuming you stayed at Interlaken Lucerne and Zürich would be about 2 hours away by train.