In todays world, parents must be extra vigilant. Back in the day, you could count on other adults in the store (or park, wherever) to alert you or help the child.
Today you better NOT count on any adult stranger or any teenage stranger even NEAR your child. No one will help you and your child but yourself.
This is probably partly due to fear. I have seen children running off from their parents and tried helping the parent get the child back. They look at people who do that like they're child molesters and don't even say thank you.
And isn't that a sad commentary on what we've degenerated into?
There still are a lot of good folks. Having one around when you need them most is iffy, at best.