Hello Dawisn
I suggest the 3 days Top of Europe Winter Pass for the Jungfrau area.
For the rest of the days, I do not know yet as all depends on the length of your stay. I would have said, the Swiss Half Fare Card including complementary Swiss Family Card. But if you only stay in Zurich, the Swiss Half Fare Card is not worth either.
I wondered why you want returning to Zurich for New Year? Family reasons? If not, there is no point in going to Zurich. New Year is not really a big event in Switzerland, especially in cities, apart from the fireworks display in Zurich after midnight; shops and attractions will be closed from 31 DEC late afternoon including 01 JAN / 02 JAN. You would better spend the New Year in the mountains, there is where people spend New Year. Your 8-year will be bored to death in Zurich while I do imagine he/she will absolutely love sledding and playing in the snow. Snow in the cities is very unlikely to happen.
See the TripAdvisor Switzerland Forums for more advice on what to do in Switzerland. Here, we are the ticket experts.
Best regards,
Roland