The children all hovered excitedly near the Little Peoples' Winter House as one or another of them read Grandma Elfra's message out loud.  Then they had to figure out what a "box that holds winter" and "smelly boxes that go fast" were.  As soon as someone had an idea, they all chased maddly after each other to see if the idea was right.

(Hint:  "box that holds winter" = refrigerator / "smelly boxes that go fast" = cars)