where did you hear that? Mothers are not allowed to harm their children at ANY time. Sometimes there are illnesses (PND being the main) which may cause a mother to suffer a chemical imbalance which means she can lose sight of reality. In very few circumstances a woman may cause injury to her child and this is an awful scenario.
Saying that they were not in their right mind and therefore treating it as manslaughter rather than murder is not quite the same as saying they're not liable
"In recent years it has become very rare for a mother who kills her infant child to receive a custodial sentence, save in very exceptional circumstances."
What happens is that they harm the child and then claim it was Post Natal Depression so getting off scot free. - a bit like PMS really - " its my hormones not me ! "
I was in my doctors surgery there and there was a leaflet entitled "It's Not OK to Shake Your Baby". Are people so mental they need a leaflet to tell them that?