Family travel around Interlaken - which pass ?

We arrive in Interlaken by car on 24/9 and will stay four nights before driving to Zurich airport where we will drop off our hire car. We plan on doing the amazing train trips up the alps as well as lake boat rides. Is there value in buying a Swiss travel pass in order to get the Family Travel Card? Thanks for your advice.

I have for the past 2 years stayed by Interlaken with my 2 kids. I get the half fare card and the free family card that goes with it. It has saved me a fortune. You break even with the Jungfrau trip alone if that's on your agenda. But then also every cable car, cog railway etc. the kids just jump on for free and you only pay half. You'll just need to work out which trips you plan to do and get a rough idea how much you would be spending without it - if you don't plan the Jungfraujoch it's probably a closer call as to whether it's worth it or not, and if the weathers bad you may end up not doing that trip.