We moved into our current home when my older kids were 8 and the younger ones were an infant and two. The older ones have been playing outside since we moved in. During that first year, they were allowed free reign of our fenced-in back yard and out front, I would pull my car across the bottom of the driveway and could see and hear them out the window in front of my desk.
My younger guys are now 5 & 7 and they have been playing outside for years. In the back yard, since age 4 at the oldest (but the older kids are usually there too and I can see them from my kitchen window) and in the front yard, just for the past year and really only to bike and play basketball and hockey in the driveway.
It's too bad that perceptions that the world is a scary place are causing people undue alarm about their children's safety. It's really not worse than when we were kids. Every neighborhood is different, of course, but I'd be more worried about safety from a traffic and injury standpoint than "stranger danger."
To the moms who answer never...you do realize that your kids are going to drive and leave home one day, right? I have a friend who won't let her 13-year-old daughter (almost 14!) walk 2 blocks to my house in the middle of the afternoon on a well-populated but not heavy-traffic street filled with parents walking their kids home from school. I have no idea what her mom thinks will happen in a little over two years when she gets her learner's permit or how she expects her to be able to earn money baby-sitting when she isn't allowed even the smallest bit of freedom and responsibility. You HAVE TO let them have some freedom and responsibility as kids. In the absence of extremely unsafe circumstance, pre-teens and young teens should be able to walk and bike places. Tweens should be able to go outside without a parent literally watching them every second. This is how they practice judgment, test boundaries, and prove that they are worthy of ever more independence. Seriously, re-think the "never" comments as they're just not based in reality.