Ride the cablecar from Wengen up to Männlichen. There is a wonderful playground up there, with a huge cow the kids can climb through. My grandchildren loved this place.
https://www.maennlichen.ch/en/summer/experiences/alpine-herdsmans-playground.html
Then if you want to continue to Grindelwald, you can either take the gondola down from Männlichen, or walk the scenic path (about an hour) to Kleine Scheidegg, and take the train down from there.
Note that a cablecar (Luftseilbahn) and gondola (Gondelbahn) are different. The cablecar or aerial cableway usually has two large cabins that run at set intervals, starting from either end (every 20 minutes for the Männlichen cablecar). The Schilthorn cablecar it this type. A Gondelbahn has smaller cars that run continuously—- you get on as it moves. The First lift at Grindelwald is this type. Männlichen has both types, one coming from each side. If you are a skier, you might have ridden a gondola at Whistler, or a cablecar (made in Switzerland) at Snowbird.
https://www.maennlichen.ch/en/summer/information/timetable.html
There is a Rodelbahn ( summer life) at the top of the Pfingstegg lift in Grindelwald.
https://www.myswitzerland.com/en-us/experiences/the-pfingstegg-toboggan-run/
Another good playground is the Flowerpark at the top of the Allmendhubel funicular in Mürren. After playing, the kids will enjoy the Childrens’ Adventure Trail for the descent, with slides, tunnels, rope swings, bridges, and obstacles. At least one parent will have to accompany them.
Here is a blog with some photos of the playground and Adventure Trail ( well-studded with ads, unfortunately).
https://bring-the-kids.com/kid-friendly-adventures-abound-in-murren-switzerland/