Hey T. -
It's hard to answer this question across the board -- kids are different and mature at different rates, and we live in different environments. Each situation they get left in is a bit different. And, local norms are different as well.
According to most state laws, children should not be left unattended before the age of 6 (some states say 7, others 8 -- California doesn't state a specific, but talks about learned behaviors and the environment).
With my children, I started leaving my son alone for a few minutes at home when I ran to the store when he was 8. Over time, this got stretched out to an hour, then two by the time he was 12. I never left him a public place until he was 10, and then only with friends. My daughter, on the other hand, is more mature at this age -- now at 6, she prefers to stay home when I run to the store for five minutes (and she knows not to answer the door or phone unless it's me and knows what to do in an emergency -- we also have good friends/neighbors next door and across the street). I certainly wouldn't leave her in the movie theater when I go out to get popcorn yet, nor would I leave her in a park -- in an open environment, more stuff can happen.
NOW -- a different topic. There are so many posts here about the increase in crimes against children and how scary the world is now, and how our children are somehow at more risk than they ever were before.
The data simply does not prove this! I want to make sure that we all understand that hearing about more crimes does not mean more crimes are being committed. We live in an age of Media Blitz, where every teacher who gets fired for fondling a child makes national news.
Ladies, for better or for worse, teachers (priests, neighbors, moms and dads) have been fondling and sexually abusing children since the dawn of time. There is no data, no sound research, that I have been able to find that categorically proves that crimes against children have risen in the last few decades. And, I have looked.
What HAS changed that may put our kids at risk -- circuitously -- is the fact that those who commit crimes against children can more easily find victims through the internet. In short, you can lock your child in her room thinking she's safer than playing at the park with friends, when in fact, she could be making plans to run away with a 30 year old male. That is a different story -- and to protect our kids from that new type of situation requires training to NEVER become involved with ANYONE they don't know on the internet!
Gettin' off my soapbox now...:)
PS Are people aware that public urination is cause for being placed on sexual predator lists in California under Megan's Law? While I think Megan's Law is great, and I use the database myself, do be aware that not everyone on the list is a 'true' sex offender -- you have to carefully read the chart for each offender -- if it states 'public indecency' or 'public exposure', you may have some drunken fool who peed outside a bar, not someone who went after a child.