We live in the middle of the woods, no roads or neighbors....just bears, etc (haha, just kidding, we haven't seen a bear in a while).
My kids are 3 and 19 months and they spend a lot of time outside fairly unsupervised. There is just nowhere for them to go but the woods. I can hear them playing wherever they are and when I stop hearing them can glance at a window (we have a VERY open floor plan and lots of windows, I can see most almost anywhere in the yard from almost anywhere in the house!). They mainly hang out by the chicken coop and wait for eggs! They are extremely patient, until they here the first cluck of an "egg song" - at which point they are in there, looking to see which nest and kicking hens off if they have to, to get to the eggies so they can bring them back to me!
I catch a lot of flack for the "free range-iness" of my parenting and I may not be so free range with the 19 month old if it weren't for my INCREDIBLE 3 year old...but they stick together like glue. She enjoys being (as she puts it) "the leader of the son" - and he enjoys following her around and listening to her chatter. So they mostly pull the wagon around and collect rocks and flowers, hang around waiting for eggs and feed the animals. They have chores that they do together (rather, DD has chores that DS tags along for) and they are really really happy when they are outside.
I can't be a hover mom, it's why we moved to the middle of nowhere. The only thing you can see around my house, is the little clearing we live in and the edge of the forest around it. By listening to the signing and talking of the children, the different clucks and calls of the chickens and the dogs grunts and whining, I know whats going on in my yard at all times.
A day will soon come when I feel comfortable NOT hearing them. My DD (without the "son") is already comfortable going to the furthest edge of the clearing, just inside the woods, to sit on her favorite rock and draw by herself. I can just barely make her out and she knows she has to be sitting on the rock in order for me to see her...I can't wait for her to be big enough to go into the woods to find things and bring them back for me. That'll be really awesome.