One of the simplest techniques I'm learning for making a nicely-lit photograph in bright sunlight, is to stick a flash aiming directly opposite the direction the sunlight is lighting your subject from, then with the subject sandwiched between the two light sources, place the camera so that one or the other light source is hitting the subject at a ~45 degree angle to the camera. The resulting wrap-around kind of light gives the subject that cool 3-D look. This simple setup results in 2 different looks: sun as backlight (sometimes called rimlight) with the flash lighting the front or, the opposite - sun as frontlight with the flash as back/rimlight.
The sun-as-rimlight / flash-as-frontlight setup is what I tried in this other shot.
In the above photo, I tried the other option since the cleaner background (trees and grass) put the sun as the frontlight. So the sun is lighting their fronts & camera left sides as it is coming from high front camera left and the flash, set up to back camera right pointing back towards the sprinkler (and toward sun's general location), is lighting their camera right sides. Focusing was a little tricky as autofocus would catch the water from the sprinkler and get confused, so I manually focused on the sprinkler (or a little behind it) and just let them run into the water and thus the focus area.
I like the way the flash catches the water spraying off of him and really makes it pop against the dark background. I only wish I didn't manage to crop off his feet while trying to get the shot without getting myself, the camera, or the flash soaked!