I spend a lot of time watching the kids. Primarily, I make sure they're safe, happy, and not pounding on one another. Usually, though, I don't play with them, as it takes more energy than I have to expend. I'm not lazy; I have chronic pain, and bending over to play with a pool full of plastic toys is excruciating. Once in a while I do play, but generally I just sit and supervise. There's a problem with this method, however. It's boring.
Today, the kids and I got out the new bigger kiddie pool (thanks Amazon!) and filled it up with water. They busily filled the pool with bathtub toys and put on their swimming suits, even though the freshly filled water had to be about 50 degrees F.
While I watched, I amused myself with photography: playing with the depth-of-field, getting the autofocus to behave, and shooting macro shots from my perch on the front porch. Result: the kids had fun, and surprisingly, so did I.