First, we start by observing the water using objects. Touching with a stick, tossing in leaves or rocks are all early stages of exploration. It's about what will happen to those objects. Do they get wet? Do they float or sink? Would the same happen to me?
The next stage is testing the boundaries. "Will mom/teacher mind if I stick my hands or feet in?" If it's a nice day, why not? This is science after all!
Since further exploration has been okayed, the next stage is discovering what the water will do to them and how it feels. Usually hands go in first, but in this situation, it was the feet.
He's discovered that his pants are soaking up the water causing more of him to be wet then what's emerged.
Now let's see how it feels on our bare skin. Also, what's down there? Anything interesting?
Now we test movement in water. What happens when I run in it? What happens if I jump? Will I splash anybody? How big of a splash will I make?
Finally, all inhibitions are lost. Our discovery is water is wet and fun. Some items float, some items sink. When I jump into the water, I make a bigger splash then simply running in the water. If I jump from a higher place, my splash is bigger then if I stand in the water and jump. Water makes my clothes and shoes wet. Water makes me wet!
Sometimes we forget to let our children explore and experiment. We can get so caught-up in the what-ifs that we forget what it was like to discover new things as a child. Sometimes we just need to sit back and let our kids be kids. You'll be surprised by what they learn if you do.