This just demonstrates the utter fuckedup-ness of the supernatural world. Clued in people not telling their kids about basic dangers--even if none of the Carpenter children had any magical talent they could easily meet some random kid who does. Just knowing that yes, really, someone using magic in certain ways is very likely going to be a seriously destructive person to be wary of seems pretty simple?

Abstinence-only magical education! Or maybe that's giving them too much credit?