Does anyone else have this same concern about your young kid?

My daughter is 5 and Most of the time I know she is safe at school. However, I always worry about someone coming and abducting a kid from school, its so easy to do. they can snatch them from the fence at recess or pretend to be the dad and sign them out at the office (they dont even ask for ID or check the emergency card) Does this happen often, i mean children getting taken from school, just curious? and have you ever feared this very thing?