SAFETY FIRST: Don’t Leave Your Kids Near Judgmental Strangers.

As a child, Ashley Thomas loved to go by herself to a meadow about a 10-minute walk from her house in Ojai, California. Playing on her own let her imagination soar. “You can pretend you’re the Queen of Sheba,” she says. Exploring made her feel independent and grown up. Once, when she was in about the first grade, she even found a snake. “There’s no way I would have picked up a snake in front of my parents,” she says. “The reason I knew it was OK was I had also gone by myself to the library to take a snake safety class.” (Yes, a snake safety class.)

Ah, the olde-time memories of the days when kids could play on their own without someone posting a video online to shame their parents — or calling the police to have mom arrested and the children seized by social services. But Thomas isn’t an aging baby boomer telling tales to her grandkids. She’s just 30.

Only in the past decade or so has “no child left alone” become the social and legal norm in the U.S. A doctoral student in cognitive science at the University of California at Irvine, Thomas is the lead author of a recently published study designed to understand what’s going on. After all, under most circumstances, the objective risk to children left by themselves is extremely low. The chances that a stranger will abduct and kill or not return a child — the great fear driving the new norm — is about 0.00007 percent or one in 1.4 million annually. It’s much more dangerous to drive a child somewhere, or even to walk with one across a parking lot, than to leave a kid alone in a well-ventilated car.

These are the Crazy Years.