I don’t really know why a book about some legs and grass would become an international bestseller, so I think this book is one of those logic puzzles like when a man dies in a glass of water because he tried to stay in an infinite number of hotel rooms. Why would you slap a child who is not your own when everyone knows it is only fun to hit things that are related to you?
Perhaps the man has gone back in time and the child he is slapping is himself because he has quite severe personality issues and needs to literalise them. Or maybe the child is a dwarven terrorist. Or a ghost.
Anyway, when you work out why the man hit the child you win a golden rabbit or some cigarettes I expect.