3Minnies1Mickey and JustAKid are both correct.
As 3Minnies1Mickey said, if you can manage weekdays, those will be better than weekends. Also, reports have been that as soon as Thanksgiving weekend ends, things quiet down in the parks considerably in that next week, until the Candellight Processional.
JustAKid is also correct in that there are no real, absolute low attendance days during the season. Yes, you can catch the parks at times when it might be slightly less busy than other times, but the holiday season is tremendously popular (last year was the busiest holiday season at DLR in 10 years). I think that the first couple of weeks of December - until around mid-December - are the best options in terms of going in December. Once mid-December hits and the weekend right before Christmas rolls around, it starts to get steadily more crowded, reaching its peak in the week between Christmas and New Year's.
Also, as JustAKid mentioned, there are extra elements involved this year that were not present last year, such as World of Color. We don't know how that will affect crowds during the holidays - when the holidays are already busy to begin with.
For example, it is now Halloween Time at DLR. In the past, the last week or two of September have not been that busy - even though it was the start of Halloween Time. Usually, crowds pick up in October. But there have already been reports that this last week has been very busy on certain days, with the lines for rides exceeding expectations. I think some of that has to do with more people having AP's. Some of it has to do with World of Color increasing attendance in both parks since its debut, and some of it has to do with people just loving Halloween Time and making a trip out to partake in the festivities (even if they don't have an AP).
Christmastime will be busier than a non-holiday period simply because it's Christmastime. But I think your planned dates will be fine!! I don't think it will be 'slow' or totally uncrowded, but you won't be there for the peak of crowds!