"Hello, my dear, kill me gently
A burned body doesn't leave you".
Means that there is no physical killing done, because a dead corpse you have to get rid of, and eventually the police or other authorities can trace the killing back to the murderer.
Someone that the child loves does not really care for the child, and treats him/her badly; the death that is inflicted by said apathy is worse than one physical death because it can keep on happening.
Maybe the apathetic person is even torturous, their only goal to hurt the child. I shall leave that open for the interpreter to decide which is the worst mental 'death\'.