I agree jtp - I have a 10 year old and a 9 year old who definitely know right from wrong and are really well behaved. I cannot rule out that they could do something impulsive that would have severe circumstances that they would not necessary foresee. They are not yet able to see sufficiently that sometimes your actions have greater consequences.
However, I also know of some kids younger than them who cause real problems with violence and vandalism that they must know is wrong.
It's not a one size fits all situation. There is no button in their heads that magically switches on at a given age.