This used to be our favorite time to go. Since our schedules have changed we can't go this time anymore. We've been during Labor Day Week-end about 12 times, although I want to add that we have not for the last 3 years or so. Labor Day Saturday is the worse time, espcially the MK. Also DD is packed at night. A lot of locals go at night and the area is very crowded. Labor Day Monday is not bad, in fact we always loved that day. This could have changed though during the past few years. I have noticed a big increase in crowds especially in the MK at ALL times of the year. If you have park hopper passes you can always go to another park if the MK is too much. Also past the week-end it does get much less crowded. Yes, people don't take their kids out of school yet, too early in the year. Hope this helped.
Have a Wonderful Vacation!!