It's vital to encourage good habits of children in their early years as what they learn now will stay with them for the rest of their life. I'd suggest keeping things positive, and setting strong ground rules - if they misbehave, they will miss out on something they really want. Explain to them why they are in the wrong and discuss alternative options for how they could have handled something better (and why this would be better for them). And reward them for good behaviour. Also, maybe involve him in community projects so he enjoys helping others - this could be good motivation. If this doesn't have success, take them to counselling for additional help. Good luck!