Travel in and around Interlarken

hi. I m travelling with my husband and 3 children (10, 7, 5) to Lauterbrunnen by car in two weeks time. We want to go up to the Jungfraujoch on the train. In addition maybe one or two other short train journeys e.g to Grindelwald and a cable car ride etc. I am really confused by all the different train passes. Is it worth us getting a pass at all - other than maybe the Junior travel card. - or should we just pay for each journey we want to make. i don't want to spend more than we need to.

Any help would be appreciated

Thanks