You'll be there in one of the highest crowd levels of the year, so I'd seriously consider 4 days or more. The days will be longer, but so will the lines! I'd expect the 50th celebration wave of attendance will still be in place, making the crowds that much larger in parks that much smaller than what you may be accustomed to at WDW.
If your DSs will let you, focus on the uniquely DL things: Fantasyland, Indiana Jones, Toontown, etc. If you aren't trying to do everything that will help a great deal.
Study DL's fastpass system (search for Hydroguy's posts/threads along with darkbeer's--two FP Masters
) and work the system, which is a little different than WDW's. Consider RideMax, a touring "optimization" program (
http://www.ridemax.com).
My family spent three days in mid-December during a pretty low attendance time and we (OK, **I**) didn't feel like that was enough time. I didn't get enough magic and we didn't get everything experienced. I know that our pokey DS5 and two 70+ indulgent grandparents
(was that redundant?) affected our touring speed which went from casual to positively sloth-like (maybe I'm exaggerating here--I have a caffeinated personality
). Are your kids motivated?
There's my much-more-than two cents worth. Happy planning!