When we suffer it is for our own good, as hard as that may be sometimes to believe. That does not mean we should seek out hardships or inflict suffering on others, it means we must accept the crosses we are meant to bear in life as the Will of God.
Christ suffered on the Cross for our good, and our own sufferings are trials and tests that can purify us and help us to look to eternity instead of prizing this world too much.
As for parents who are cruel to their children, yes, unfortunately it happens a lot, but at the same time children must be taught to respect their parents and to respect others, this requires suffering consequences for misbehaviour.