First, I see that you are new - welcome to the forum. I hope you like it here. It can be a very good source of information.
Next, to your question. The week after Christmas is the busiest week of the year every year, bar none. The web site of the Unofficial Guide to WDW that predicts crowd levels (
http://www.touringplans.com/BestDays.htm) had the levels that week to be nearly all 9 and 10 out of 10.
I have never been to WDW this week, but I have been there during weeks in the summertime that are crowd-level rated mostly 8 out of 10.
So, let me say this: if you go to WDW this week without doing a significant amount of planning, and familiarizing yourself with the ins and outs of WDW, you will almost certainly not have a good experience.
Having said that, I have heard that the Christmas decorations and special activities are very charming at WDW. So much so that some people go every year, regardless of the crowds. And if you plan your trip properly, you can probably have a very enjoyable trip.
Having a touring plan of the parks during very busy times is essential. The key is getting to the parks early every day you visit, making a plan tailored to your families preferences, and knowing where to be in the park at any given time of day. Sometimes this will mean taking a break mid-day, when it is most crowded. Also taking advantage of the Extra Magic Hours available to resort guests.
No one touring plan is right for every family. The best advice I can give you is to get a copy of the Unofficial Guide to WDW and read it. Then decide if it is worth it to you having to do all that planning and following it as closely as you can (and still remain flexible enough to modify it as you go when necessary).
You say that your child is 8 years old. An alternative is to pull him or her out of school for a week. Dec 5-9 would be ideal. The crowd levels are expected to be 1 out of 10 almost that whole week, and many of the Christmas decorations and activities will already be there. Have your child's teacher give him/her some work, and spend a little time each day on homework. I would have trouble myself pulling my kids out of school past sixth grade, and would hesitate starting in fourth grade, but at 8 years old, I wouldn't think that it would be a problem. But that is a very personal choice.
Going this week, you would hardly have to do any planning at all, and would be able to just go with the flow and relax. Although you would have an even better time if you do at least some minimal planning.
Another thing to consider is going during a week that your child will already be out of school for part of. For example, each year in early November in New Jersey, there is a teachers' convention on a Thursday and Friday. We are considering going during that week so that our kids only miss three days (they will be 12 and 8 - no problem for us for the 8 yo, but hesitating on the 12 yo - but I think it would be OK).
Good luck, and I hope you have an enjoyable trip if you decide to go, no matter when that is! Please feel free to post more questions and everyone on the forum will try to be very helpful.
P.S.; here is a link to Amazon.com to the Unofficial Guide to WDW (I'm not particularly endorsing Amazon here, this is just a reference to the book so you know what I'm talking about)
http://www.amazon.com/exec/obidos/t...f=sr_1_2/002-5663103-3268840?v=glance&s=books
It is also available in many free public libraries. If you decide to actually go, especially if you decide to go the week after Christmas, I would highly recommend getting your own copy. It is the best guide for park itinerary planning and has a wealth of other useful information.