We have spent New Years Eve at HH for the past two years, and have reservations for this year as well!
The 2002, there were two parties for kids: one for those up to age 12 and one for teens. In 2003, they broke it into three age groups. I can't remember what the exact breakdowns were, but I know that it seemed to work out better for everyone.
There were no planned activities for adults, which was fine with us. We have never liked going out on NYE because of all the "crazies", so we have our own routine of having a nice dinner and champagne at midnight. We have just moved that routine over to HH, LOL!