Consultant Marc Armitage's study of 60 UK primaries suggests stories with topics such as murder and cannibalism are common in children's play.
But he found that, while the dark themes may disturb adults, the children who created them remained unaffected and could distinguish between fantasy and reality.
"This form of play may be a psychologist's nightmare, but this does not worry the children who engage in it. Nor does it turn them into murdering cannibals as adults," he said.
The study, "Sticks and stones may break my bones: violence and evil in the play of children", was presented this week to a conference on play, in Sheffield.