a child called "it"

I recently started to read this book. some friends had to told me that i should because they had really liked it even though it was really sad and violent. 

im about halfway through reading the book. it is honesty shocking to read everything that the child suffered through. 

I don`t understand how someone so loving and caring could change so drastically and even more towards her own child. How could any human be so cruel to another human being. i`m not sure if i missed it or what but i don`t understand why the mother changed her feelings all of the sudden the way she did. at first i thought it was because her husband has left her but that`s not it. so i`m still wondering about that. 

I`m frustrated, mad, and discussed about the mother. But i`m even more mad at the father for letting it happen. At first he was unaware of what the mother was doing to one of his three children because she only did it when he was away somewhere or when he was working. But later he found out what was going on and even though he argued with his wife about giving him those punishments he never really tried. yes he would "lose" in their arguments between each other but he still could have done other things like call the police or report it as child abuse. Was this man scared or afraid he might get punished too for something  he didn`t do? At the beginning he might of not but in the middle when he just stood there and watched his son swallow Clorox or other household cleaning products and watched as his son fought for air and did absolutely nothing to stop it, then he would have gone to jail also. 

This kid was very brave for having the courage to try and survive  and win this battle against his monster mom. I`m eager to finish this book and find out what ends up happening to his parents.