I don’t know if this (described below) would be do-able at the time of year you’ll be in Wengen, but the following is a write-up I shared October 7, 2019. It’s a fabulous hike above the Lauterbrunnen Valley (basically parallel to the Lauterbrunnen - Stechelberg very flat valley walk, but up higher and with drop-dead views). It meets all of your criteria, if snow isn’t a factor when you go. ‘Just a tremendous hike!!
There have been numerous mentions on this fabulous site of the nice, basically-level walk between Murren and the station at Grutschalp (<— which is across the Lauterbrunnen Valley from Wengen). I agree that it’s an enjoyable stroll, and it certainly is an appropriate choice with kids or with elderly family members. But a *really* lovely alternative is the trail that pretty much parallels that one, except higher up. On the yellow trail signs, it is referred to as the “Mountain View Trail”.
If you don’t mind a bit of exercise for your legs going up the initial section (which begins on the uphill side of the rail tracks at Grutschalp, and initially goes uphill into evergreen woods from there; but not for any interminable length, and you’ll have shade to keep you cool), you will be *more than amply rewarded* by a beautiful, open trail above tree-line for several gorgeous hours afterwards, with stupendous alpine mountain views the entire way, and ending up at Almendhubel, where you can then either walk, or take the gondola, down to Murren. The best time to do this route is in the afternoon, when the sun is shining right onto the Alps (Eiger etc), making them pop out from the sky beyond. (Morning is much tougher for pictures, if you take as many as we do. Tough exposure in the a.m.). Just be sure to check what time the last gondola leaves Almendhubel (in September, it was around 5 pm), for your trip down into Murren at the other end.
We’ve done this route on its own, but we’ve also done it with several variations:
>> walking all the way to Murren (which is a nice add-on, being very pastoral and all gently downhill)
>> combining it with a ride up Schilthorn afterwards (which means, though, that you don’t have time to do the trail in the afternoon, when the Mountain View Trail is at its best).... An option could be to do Schilthorn first, and then do the high trail from Murren back to Grutschalp in the afternoon, although we found it most enjoyable in the opposite direction
>> doing a full loop: first on the higher Mountain View Trail from Grutschalp to Murren, then walking back on the level, lower, much more populated path from Murren back to the Grutschalp station
We’ve done all of these variations. What we loved was:
— the Mountain View Trail is not nearly as populated and well-traveled as the lower, level, busier route
— it’s much quieter, and you’re never looking at railroad tracks as your view
— except to initially get up to the rest of the trail — (the wonderful, extended, horizontal part) — the view is never obstructed by trees
— you walk through lovely green pastures, and come upon terrific lunch spots with drop-dead gorgeous views
— you can tailor the length of the outing to your energy level and time available
We were surprised that this trail is not more widely written about in the local information. It’s just lovely. The Mountain View Trail itself takes 2-3 hours, depending on how much you gawk at the views and how many pictures you stop to take. We couldn’t resist. The seemingly-always-very-crowded Grutschalp cog-train / gondola was the only downside... You get spoiled being out in all that Nature on the trail. But if you can squeeze over to the right-hand side (going down to Lauterbrunnen), you’ll get more amazing views then, too. And again, if you want the option of taking the gondola from Almendhubel into Murren, check its timetable in advance. It’s more limited in its schedule than the Grutschalp end of things.
’Hope this encourages you to give this route a try. You won’t be disappointed. : )