If you can read any Japanese at all there is a really cool interactive map of Kawaguchiko, where clicking on the little green dots links you directly to the hotel/ryokan's website. |
But if that is of no use, www.japaneseguesthouses.com can help or so can rakuten travel or the like.
I have no kids but I have found that we encounter kids more often in more modern, hotel-like places.
We have personally stayed at Konansou at Kawaguchiko and had a wonderful view of Mt. Fuji from out room. The baths also have spectacularly views and there is a foot bath up on the roof from which you can see both Mt. Fuji AND the lake.
Places on the north side of the lake have views that are better, looking across the lake to Mt. Fuji. But at Konansou, you can get a room with a private bath with a view of either the mountain or the lake. We were pleased with the service - dinner was in a very pretty private dining room, and there was plenty of parking, if that makes a difference.
The lobby was a bit garish as I remember. Don't let that put you off.