jim,
Before deciding which pass would be best value, you'll have to give some thought on which sights and which mountain lifts you'll be using in that area. One of the other Swiss Passes or the Half Fare Card may also be a good fit, depending on your sightseeing. The issue of picking "the right" pass for Switzerland is usually very challenging for most of us, and some have formatted an Excel spreadsheet to try and make some sense out of it.
This website might provide some answers - https://www.ricksteves.com/travel-tips/transportation/trains/switzerland-rail-passes
I've never travelled with children, so not sure what discounts might be applicable for your 8 year old. I'm sure one of the others can provide more information on that.
If you're planning to visit the Jungfraujoch, a couple of other important points to mention......
- it's a good idea to check the weather prior to making the trip, as you won't be able to see much or venture outside if the top is shrouded in fog. If you're planning on venturing outside at the top, be sure to have appropriate clothing.
- Especially with an 8 year old, be sure to give some thought to the altitude of the Jungfraujoch (about 12,000 feet) as that could present some problems. In the same situation I'd discuss this with my child so that h/she can tell you if they're having any problems.
You could also consider a visit to the famous Schilthorn and Piz Gloria, which was made famous by the James Bond movie On Her Majesty's Secret Service. You might find it fun to watch the movie before you go. The cable car ride to the top is spectacular! The Schilthorn is at about 10,000 feet so not as much of an altitude issue. There's a good (albeit pricey) revolving restaurant there as well.