Why was Christian Bale slapped in empire of the sun isn't it too early for child actors to get into acting only to immediately to get slapped?

Why was Christian Bale slapped in empire of the sun he was, only 13 years old and it was only his first ever acting debut role, he has never done any acting before, isn't it too early for child actors to get into acting only to immediately to get slapped, why did Steven Spielberg ask the actress to slap him, shouldn't it be illegal, and am I the only one who hates that they use method acting and feels sorry for him