I've put these photos together to illustrate the effect different natural lighting types. The photo on the left features the small child entirely in the shade. The trees are quite high above him, so it's bright enough for a photo, but there's no direct light. In the right hand pic, he is in direct sunlight. The parts in the sun are washed out by the brightness, and meanwhile the features in the shade are rather flat. And then the camera gets confused as to what what balance to use (should it err on the cooler side to compensate for the warm sun, or vice versa?)

That is the brief version of why I recommend taking people portraits in the shade, unless you're using a selectively metered flash (to lessen the contrast between sun and shadow) or unless you're intentionally creating a sun and shadow effect.

Two year olds just keep on movin'. I took the flash off my camera, because it was too clumsy to keep on the camera (the external camera flash is heavy and unwieldy), while chasing this little guy around. I just hoped that he would pause long enough in shady spots that I could grab a few quick photos.