By age 8, most children know the difference between fantasy and reality, according to Communication Arts Professor emerita Joanne Cantor.
Plus, Cantor says, there are usually counter balances in children's lives that help them further decipher make-believe from real life.
She says the case in Waukesha where two 12-year-old girls are charged with stabbing a friend 19 times is also rare, because neither girl seemed to have interjected a reality check or told a third person about their saga.
In the criminal complaint, the two suspects said they had been planning the stabbing since December, in order to please an online fictional character Slender Man.
Cantor says children generally become competent by second grade at deciphering fantasy from reality - they know longer believe, for example, that the wicked witch exists. However, Cantor says, by the pre-teen years, children understand that while a fictional story did not happen, they realize something comparable might occur in life - such as an adult harming a child, and can react in intensely to that knowledge.
But the professor says in most cases, children have other influences in their lives that inject reality.