That is really the saddest thing to me. I remember with great amounts of happiness when I was between 5 and 10 years old and would ride my bicycle around the neighborhood with my friends, go traipsing around the woods, and exercise my imagination. (Getting home and having to sit still while my mother dug through my hair and scalp for ticks was torture, but was worth it.)
My nephew is not yet four years old, so he's probably still too young to be outside playing on his own, but I fear he'll be in the same boat as your daughter in a few years, unable to do anything outside of his parents' line of sight.
It's much safer to be a kid now than when I was growing up, but the news makes it seem like it isn't. I would let my seven year old walk to the park by herself, 1/2 a mile away, if I wasn't afraid of having the cops show up.
When I take her to the park now, I let her play on the structure about 100 yards away, within my line of sight. And still adults will come up to her and ask her where her mommy and daddy are.