Both, but to be honest, it is more common for boys to fight, especially so close in age. You have to take into consideration that boys in general are rougher and that being so close in age, they are going through their natural stages. Discipline is definitely needed. I would also suggest getting them involved in sports together. If you can afford it perhaps karate or martial arts, or when older, sign them up for youth wrestling. I personally have found myself LOVING wrestling. It is a great way for them to use up energy, and get out aggression in a way that is safe, trained, and controlled. And the best part is, they can practice at home together. Just make sure you pay attention at their scheduled practice. Then you know what is right and what is wrong.