We did a week in Wengen last summer with 3 teens. Have been there many times before but not in summer since they were little.
We mixed chilling out and hiking with a couple of 'big ticket' days.
Rafting down the River Aire from Uttigen to Bern was a hit with everyone. Takes a couple of hours, you just float down, can pull up to the side at any point for a break/picnic and as long as 1 person stays in the boat, the others can jump in the river and swim/float down at the same speed as the boat. You set off from Uttigen train station and can then get the train back from Bern.
A couple of us did paragliding from Murren, also excellent
Others of us hired bikes from Grindelwald and headed up to Grosse Scheidig. They had regular push bikes and it took them about 5 hours to cycle up and less than 30 mins to come back down. They are keen cyclists. I would recommend hiring electric bikes!
There is an outdoor swimming pool in Wengen, with a stunning view that does surprisingly cheap food for the area and is a sun trap for much of the day. Also in Wengen a pretty decent crazy golf course (better than the one in Grindlewald)
Lauterbrunnen is very close to Interlaken on the train but if you're going to head that way, I'd go further and go up to at least Wengen or Grindlewald, or Kleine Scheidig. Don't just stop at Lauterbrunnen.
I'd also take at least a decent pair of trainers, you will do at least some walking even if you're not hikers
Be prepared for everything to be sooooo expensive. It just is.