What gets me is beating a baby? Beating a child any age (and adults of course) is inexcusable but how fucked up in the head must you be to look at a literal baby and hate them so much (and it really sounds like she hated him) that you hit them, regularly? For doing normal baby things? Pure evil.
What makes it worse somehow is that she and her husband were going through the adoption process, they could have changed their minds at any time and someone else would have fostered the baby, no doubt about it.
whatever the reason this lovely, gorgeous little boy was removed from his birth family, I hope they are getting lots of support, especially his birth mother.