I Have A Theory About Little Kids
Here is the Boy last week at the playground, looking like a drowned rat. In this picture, he is soaking wet from having run through some sprinklers. He is also a bit muddy. And, when this picture was taken, he had also had an accident in his big boy Curious George underpants.
If I was soaking wet, muddy, and had wet myself, I would be very uncomfortable, and very grumpy indeed. Not the Boy. He was as happy as a clam.
I think what makes adults comfortable is the opposite of what makes kids comfortable. It's the only explanation I can think of as to why the Boy is so happy being dirty, hates getting clean in the bath, and likes to sit in his own filth.