Of course it will be different if 是繼父. What is your point?

You should know, except extreme cases, biological parents love their kids more than anybody else in the world. That does not mean they do everything right as parents; but still, kids can feel their love. 

People do NOT think it is right to slap the kid. At same time, we do not think the father is abusing the child; at least, not from the limited info posted. (The father does need to change the way he disciplines the child.)  We feel, for kid's welfare, it is better to work this out inside the family than involve police.