A 9 year old is old enough to be responsible to be alone, but not old enough to fend off a kidnapper. Hence the caution.
But you need a reasonable level of caution. Across the entire country of Canada, there's about 25 kids kidnapped by strangers every year. The dangerous part is his getting hit by a car while biking the two blocks to the park, not someone trying to grab him while he's at the park.
Back in the day grandpa Tom or Uncle Fealy weren't considered threats, kids weren't taught to keep them from touching, and mom's weren't plastering counters with antibiotics. We used to fear Bears, wolves, crazy Charley, and those African Americans (yeah that's what they were called back in the day/not) in French Town. We were settled on pretty stable stereotypes in our communities (one stereotype for one community).
Sure my great great granddad ran away from the farm in South Carolina and joined up with Mormons in Nauvoo when and traveled to northern Utah when he was 16, but, that's the exception. Right? OK, maybe not.
But here we are afraid of a whole new bunch of things. We don't die when we're still able to do heavy labor or bear children any more. So, my youngest was killed by a drunk when he was 31. So what? My other kids have kids and my other kids are already older than 40 (about when the average person died in the 1880s). So we invented other reasons to fear God, dying, having our stuff taken from us, to fill the vacuum (back to the antibiotics on counters).
Hell, we lived through 50 years of DDT until we realized some of us would die from it by just eating peaches.
Fear attaches to things until it takes up all that space we've reserved, or, have been conditioned to reserve, for it. That makes it different from greed since that operates until there is noting left to desire.
Kids are just one of those things to which we've attached fear so we can feel less afraid of being killed by a lightning bolt.
added after seeing other posts.
Oh come one. There used to be white slavery all over the US and Europe and society wasn't all that concerned. Our unconscionable fear of such now is part enlightenment and part fear farting. Women have rights now so women are seen as having some value now. Enough said. The fear farting part is excessive fear by such as: those fundies who used to sell their daughters into slavery or have them taken out by wolves and who are not wringing hands to get others to come to church and sign up for mean spirited issues like keeping poor women from avoiding having unwanted children; or, those do gooders who wring their hands for every poor child thinking it is being abused.
