Our family have been going to NASPA in Yuzawa the last few years and having a wonderful time. It is quite expensive, but a lovely holiday if you are looking for a convenient family ski resort.
They have 3 New Zealanders working there in the ski school this year, and a child care facility, so it is a place where you can leave the kids if you want to go off and enjoy the day. Quite a few foreigners go to the resort, so they are fairly used to dealing with foreign families. Recommended.
The website is here http://www.naspa.co.jp/english