Kusatsu

Hello,
Is Kusatsu a good town to visit for its onsen and snow playing?
We, with 2 young children, plan to be in Tokyo during mid Dec. and plan to spend 3 days in disneyland / disneysea and we have another 4 days before we depart from Tokyo to Singapore.
As we have already visited Hakone and Nikko during our previous trip, greatly appreciate your advise on places we can visit for this trip. We would like onsen and definitely snow and would like a very leisure relax trip.
Thank you.

Yes, Kusatsu has the best hot spring waters in Japan. And it has also a high probability of snow in mid December. I think you would enjoy it. I recommend to spend at least one night:
http://www.japan-guide.com/e/e7400.html

Hi Uji, any recommendation on the accomodation in Kusatsu which has easy access to the ski resort and onsen?

Any other places along Tokyo and Kusatsu which we can visit?

I enjoyed my stay at the Naraya, a traditional ryokan just a few steps from the yubatake:
http://www.kusatsu-naraya.co.jp/eng/index.html

There should be some kind of shuttle buses to the nearby ski resort.