I would be fine at age 2/3 if we didn't also have a pool. Our pool has a extra kiddie fence around it but you can never be too careful with kids and water. My husband is so paranoid and doesn't like the kids in the backyard at all without supervision and we have a mature 5 year old. He is afraid of kids getting taken.

According to Fairfax County: 8

https://www.fairfaxcounty.gov/familyservices/children-youth/child-supervision-guidelines

Age Guidelines
8 years old and younger should always be in the care of a responsible person. Children this age should never be left unsupervised in homes, cars, playgrounds or yards.
9-10 years old may be ready to be left unsupervised up to 1.5 hours during daylight and early evening hours.
11-12 years old may be ready to be left unsupervised up to 3 hours during daylight and early evening hours.
13-15 years old may be ready to be left unsupervised more than three hours but not overnight.
16 years old and older may be ready to be left unsupervised overnight for one to two days, with a plan in place.


For what it’s worth, when my children were younger (they are in college now) the County started with Age 7. At some point, they increased the age to 8.

I did agree 3 with an open window and trusty dog outside

2, fully fenced with locks on gates, keep back door open so I can hear her while I’m in the kitchen. I look out often. The dog is out there with her.

I still don't let our 4 and 6 year olds play in our backyard alone. We live in Del Ray and our yard backs to an alley that people use as a cut-through. Also, our land is sloped and the backdoor is up a flight of stairs and across a deck - so it feels pretty far away.

This really depends on the outdoor space. Ours was childproofed and fine for out almost 3 yo as long as we were within earshot. She could happily play in the sandbox or watertable while I did dishes. An unsafe or unfenced space is completely different.

Does watching from the kitchen count as alone? If so, whenever they are fine with it (age 3ish?). If you meant outside alone, as in a neighbor's front lawn without the neighbor necessarily keeping an eye (but still a familiar, low risk environment), perhaps 6-7?

My DS could be trusted to do this around age 3-4. At age 7 he could ride his bike up the street to the neighbors and circulate between a few friends' houses. I also share concerns about distracted drivers but I'm not sure that's a reason to keep him home.

My 5 yo DD, A Hellion, still can't be unsupervised. Tried it out and looked out the window to see her disappearing into the depths of the woods behind our house by herself (she climbed the fence). So, nope.