You must have misread something. The concern isn’t nebulous adults in white vans, it’s the “friendly” neighbourhood busybodies saying “do you really think you should be letting your kids roam free” that people fear. Social pressure is a hell of a drug.

Yeah, it’s nonsensical, but such is people. Similar to why most people aren’t having children in their sexual prime, instead waiting until they are of geriatric age. The harsh reality is that society says it’s wrong to have children “young” and ostracizes anyone who does. Just ask any teenage mother about the scorn they had to deal with.

Thousands of years ago most people didn't have time to sit around and evaluate what other people do. Only the richest kings could even begin to live in that kind of luxury. And even up until around the 1950s, most people lived rurally, so the kids weren't apt to leave the property anyway – and if they did, who was going to see it?

Not to mention that there wasn't the "You must go to university or you will ruin your life" nonsense that has emerged in the past ~30 years. Hell, in my grandparents time, it was uncommon to even go to high school. Back then, having children was celebrated, not featured on MTV with a show that tries to convince people to not have children.

Let's face it, we've collectively come to hate children, and as a result people are reluctant to have them.