This is an activity my son, at a certain age (and maybe males of any age), became passionate about. Its certainly a popular sport around here when the weather is right.
My son and his friend took the pickup and a 300 gallon water tank, and emptied it into a low spot in the field behind our house. It is not prairie. It is an old pasture full of eldeberry, milkweed, and goldenrod, but it is a lovely place and I hate to see my son use it this way, but he has to have some place where he can just go crazy and do his thing. Over the past few years my son has turned it into an adventure waiting to happen, with old tires, plywood and a tractor with a bucket attachment.
I wouldn't let either boy, or their clothes in the house. I handed them the hose and a couple of towels with explicit instructions that no mud should cross the threshold.
When i look at this photo, I think of my son as a happy toddler, just being introduced to eating food on his own. I used to keep that old photo on my cork board at work, as a reminder to how far we'd gotten. He looked about the same as this picture, but the color was red, and his hair was much shorter. He had squooshed spagetti and sauce into his hair. It covered his face, his arms, and his chest. It was all over the place. Some things change but not by much.