I would just like to state for the record that the Holiday Magic exhibit is very worth a wait. We spent 30 minutes or so waiting in line at the Botanical Gardens... Let me amend that- at least 1-2 members of the party at all time stood in line and the rest of the time adults were trying to keep the two little boys entertained, moving, and happy.
Then we headed into the exhibit of amazing little model structures made from natural sources such as sticks, pine cones, leaves, etc. The houses/ships/furniture were all built from these plant components. Then the real reason we were there- the model trains running through these little tableaus. The boys enjoyed the trains almost as much as their dad :-)
The whole exhibit was enjoyed by all and I could have spent over an hour just staring at all the details. I think I absorbed about 10% of the artistry. So for future reference if you are in the DC area during the holiday season (Nov to mid Jan) make it a point to travel over and see the Holiday Magic display... it is worth it even if there is a wait.