Heaviest crowds of the year obviously so plan for long waits.
MK does their special NYE fireworks on the 30th and 31st.
Epcot has dance parties in multiple countries and has one of the best fireworks shows I've ever seen for their NYE fireworks. I prefer Epcots NYE fireworks over MK
HS does fireworks too but it's not on the scale of MK and Epcot.
If you have really young kids you'd probably rather do MK. Just know that it will be packed and last year around 9am the line of cars to get in was huge. Epcot while there's still a ton of kids does have a lot of alcohol booths set up with champagne and beer..so I know not everyone is fine with their child being around alcohol being served.
NYE at Disney is great as long as you're prepared for the lines and the crowds