May Allah (swt) guide us to the straight path and forgive us, by the blessings of Prophet Mohammad

and his family

.
The religion of Islam teaches that children must always respect their parents, even if their parents are unbelievers or infidels. When children abuse their parents or unrightfully disappoint them extremely, they are considered as being "aaq," or disobedient/undutiful. In Islam, this is considered amongst the greatest sins one can ever make. A person who unrightfully does this shall not enter paradise if his/her parents don't become pleased.
Usually, when parents are treated so harshly by their children, they might say that they have disowned their children. If the parents rightfully do so, meaning that their children unrightfully wronged them, then the children will have acquired a huge sin. Otherwise, if the children did not unrightfully wrong them, then they're fine. For example, let's say that a father becomes outraged at his son for becoming religious or praying. In such a case, even if the father disowns the son, the son has done nothing wrong. In fact, the son receives a great reward for such a struggle.
Now if the parents do no fulfill their responsibilities towards their children, by not raising them properly or completely neglecting them, they will acquire a big sin as well. They will also be considered "aaq."
Wassalam.
M. Baqer Al-Qazwini