There is certainly a genetic component to people's behavior. Inclinations to aggression and anger have roots in the 'nature' side of the equation as well as the 'nurture' side. However, identical twins that are separated at birth will have totally different life outcomes based on the situation and skills of the parents they have. Bad parenting is the primary cause of bad children.
Children don't learn to behave on their own, they should be guided. I know in my own community we have small children who run around their neighborhood with zero supervision. They are out past dark. They ride their bicycles, sometimes even into on coming traffic. All while their parents are either at home or at work. It is unfair to blame all of these problems on the children, when there are obviously bad parents behind a lot of it.
There are bad children, but there are plenty of bad parents as well. There are mothers and fathers who drink and smoke around their kids, curse, and abuse their kids and each other. Just because a person can reproduce doesn't mean they actually should. People need to learn to be better parents in classes.
Yes, there are bad parents, not only bad children, because most children who misbehave have parents that either don't know how to parent, or didn't care to. Most parents who have criminal records will have children that grow up to have criminal records, because they are shown by the parents that it's a fine way to live.
I think that there are both bad children and bad parents. I think that a lot of the time, when a child is bad, it is due to poor parenting. I think that bad children are the product of their bad parents. But I also think that sometimes there are just bad kids.