I think it is a pulk.
Basically it is a sort of sled, where you put your baby, or other stuff you need brought with you when you travel by ski. It's also commonly used by those who have travelled in the polar areas, I've been told.
You bind the sled to your waist by the belt hanging onto those long sticks, and can bring the baby with you when you do cross country skiing, even up and down mountainsides. It consists of a frame, and some material protecting the baby against the wind. Of course the babies have to be suitably wrapped up in warm materials from beforehand, as they don't move much in the cold.
I can't see from the pictures whether Mette-Marit is assembling it or taking it apart.
A link I found explaining a bit more:
http://www.kidznsnow.com/tahoe/SITE...70/0/direct?c=1