I once called the wildlife rehab place near me when something similar happened. I was told that the fledgling's parents are nearby, watching it, and the thing to do is to put the little one IN THE SHADE in a place where the parents can find it.

Shade is critical; hot sun will dehydrate a little bird rapidly. In the case of the bluegrass festival, I would try to get the fledgling far enough away from the stage so that music and people walking about don't confuse the parent birds.

Even if the parent birds don't understand what has happened, they will find the fledgling by calling to it and listening for its cheeping replies.