Hi Sarah
I live in Bern, but I played in a band in Münsingen and know half of the people there.

There are a lot open people in Münsingen. Most people I know have older children as you've got.
Maybe you should just hang out in the Grupfti Gans. We had a few gigs in this wee restaurant. A lot open people there.
There's also a biker shop. They've got a bar outside the shop. I always made new friends over there.
I don't know where you're from, but I'm actually from Scotland and I was always the "Rock Star". Just because I'm Scottish!
There was also a pub there. (Don't remember the name). But my friends told me it changed a lot. It's not as good at it was. A lot drunk teenager.
I know that's not a help to get friends for your children, but maybe you could make some friends yourself. And they know other people... And so on.
Anyway. There's also a park by the train station with a playground.
I know Swiss are not very open people, but they are a lot more open in Münsingen as anywhere else in Kanton Bern!
Good luck!