We went on November 30th last year when the forecast called for mild sprinkles during the middle of the day. IT DUMPED RAIN!!! We finally got a reprieve from the rain around 2:30 and then only sprinkling from then on, but we were not prepared for that amount of rain.
After the initial soaked to the bone feeling passed, we had a great time. We walked onto every ride. Indoor restaurants were jammed though so try to make reservations now and cancel that morning if you don't need them.
To the OP. Make sure you bring umbrellas, rain coats, extra socks and shoes and an extra change of clothes (2 for the kids). We used the cheapo rain coats from
WalMart which were good enough. Also, bring a hat as the rain falling on your face will get annoying really fast.
The ToonTown characters were all in Mickey Mouse's which was a nice surprise. Got Dream Fastpasses on the way out which were useless as we were practically the only people in the park.