Is it wrong for kids to hit their parents? Is it wrong for parents to hit their kids?

I found an interesting article that says that kids who are hit by their parents are much more likely to hit their parents than kids who are not hit by their parents. So I just got curious about other people's opinions. If you care about the study enough to ask about it, and are also too lazy to use a thing called google, I'll find it again and link it, but don't just ask for it and never return to adjust your answer accordingly - I actually want to know people's/your opinions.