It was either 13 or 14 nights, with an almost 4-year-old and an almost 1-year-old, from New Year's Eve through the first two weeks of January. We watched the NYE fireworks from our balcony. We had booked Wilderness Lodge and due to construction (I think?) got a free upgrade to the Grand Floridian.
We went to all the parks, but most often MK. We had one weekend just at the resort. The length of stay was fine. Unfortunately, my youngest and my husband both got sick on that trip. We had a doctor visit the room and they were holed up for a day or two. We had someone banging on our walls in the middle of the night because my son was crying... believe me, if we could have stopped our baby from crying, we would have.
Of course, my daughter LOVES the memory of going to MK with just me while they were sick!
I agree with others who say longer vacations are preferred with little ones. We don't rush or feel the need to spend all hours at the parks. It's a production to get everyone packed and flights are NOT fun with toddlers (for mom and dad, at least). I've always preferred to take a longer trip and only deal with that stuff once a year or so than to do shorter, but more frequent, trips.