Why are the Dread Doctors choosing these kids?

The question came up why are the dread doctors picking those kids and I have a theory. they are all related to people in law enforcement. From the ones we know, Tracy's dad was in the van transporting Donavan, ( I think he was the DA or something) Donavan said his dad was Stile's dad's partner, and it seems that Hayden might be next and her sister's a cop. There are other kids that we don't know about, like the guy chewing the wire at the hospital and the scorpion one but I think they all might have this in common.

Just a theory anyway