Spotted

I'm working from home today. So, I've closed the door to the office and let Peter and Soren amuse themselves in the rest of the house. Out of the corner of my eye I just noticed something go by the deck outside. I looked down and this is what I saw:

That is Peter pulling his big wheelbarrow, Soren pulling his little wheelbarrow (in the second picture he's dumped his wheelbarrow into Peter's) and his sled. They are heading in the direction of the hills to the north. Any guesses on what in the world they have planned?