The sand and water table had collected lots of water from the rain over the last couple of days. My guess is Logan decided to make mud by mixing in nearby dirt. They then preceded to fling it up in the air (aiming for the house mostly). They were having so much fun, that I just let them continue. I figured it's just dirt and baths can take care of that. :)
You can't really tell from the pictures, but they were soaked, and very dirty...but they were happy.