I plan to travel to Switzerland and cover Mount Jungfrau with family in mid-June. I am split between staying at Lauterbrunnen or Wengen. As I have a young family, I prefer a location which provides me with kids friendly activities.
Rinaldo, welcome.
You don't say how old or how big that young family is.
If you want to be on the valley floor, looking up, and want to walk the kids along a river, along the bases of the cliff, and see waterfalls up close and use buses or feet, Lauterbrunnen may be for you. Be aware that there is plenty of traffic and perhaps drivers looking at the scenery.
Wengen is car-free, gorgeous views including the Schilthorn and looking up to Mürren, and is on the right side of the valley for travel up to the Jungfrau, but I don't remember much for kids there. It has always struck me in the summer as a village for older people. Maybe true, maybe false, but that's how it has impressed me.
On the opposite side of the valley, at the top of the cliffs, is Mürren. I personally believe that it has the absolutely best views in the area, looking across at the Monch, Jungfrau and Eiger - so close you think you can practically touch them, yet well protected edges with walls and guard rails. It is car-free, has a little playground near the church, the walk down the hill to Gimmelwald is really easy, paved, and safe, and there is a Sports Centre with all sorts of things to amuse kiddoes, including mini golf and giant chess game.
All three places are quite different so it is for you to choose.
I have stayed in Lauterbrunnen, Wengen and Murren. I agree with Nigel that Murren has the best views. I personally prefer staying in Lauterbrunnen as I am usually there for several days, going up both sides of the valley and Lauterbrunnen is the most central. However, if your visit is short and you are only going up the Jungfrau I would say stay in Wengen as it's a different experience staying in a carfree village which would be preferable with small children I would think. ( I think I do remember seeing a playground in Wengen)
Lauterbrunnen is a more central location, and is the transportation hub for that area. If you plan on touring both sides of the valley, that would be a better choice as it will save time and money in getting around. I don't have any suggestions on "kid friendly activities" as I've never had occasion to check that.
Thanks everyone for the inputs, it is very helpful.