An interesting discussion of the role of aggression in children in Mary Midgley's Wickedness.
We have to consider realistically the part which mild, controlled aggression actually plays in human social life. As with fear, it is probably best to start here by looking at the beahaviour of small children. At this simple, primitive end of the spectrum, stimulated attack is a marked and essential part of play. This is not because children are full of hatred and destruction. It is because the sense of otherness, the contact with genuinely distinct personalities around them, fascinates them, and it is best conveyed by mild collision. Laughter and other distancing devices safeguard the proceedings--but the wish to collide, to invade another's world, is a real one. Without that contact, each child would be isolated. Each needs the direct physical clash, the practical conviction that others as well as himself are capable both of feeling pain and of returning it. Surprising though it may be, that interaction lies at the root of sympathy. The young of other social animals play in the same mildly aggressive way, and derive the same sort of bond-forming effects from it.
Besides play, however, children also need at times more serious clashes. Real disputes, properly expressed and resolved, seem essential for their emotional unfolding. In this way they being to get a fuller sense of the independent reality of others. They find that there is somebody at the other end. They learn to control their own anger, to understand it and to reason themselves out of it. A quarrel which is worked through and made up can be profoundly bond-forming. But they need to feel anger before they can control it and to learn that it can sometimes be justified. They learn the difference between justified and unjustified anger, and come to accept that justified anger in others can be the consequence of one's own bad conduct. What they learn is thus not to eliminate anger and attack from their lives, but to use these things rightly. And in adults, right up to the level of saints and heroes, this is an essential skill. Mild, occasional anger is a necessary part of all social relations, and serious anger gives us, as I have suggested, a necessary range of responses to evil. Our linked capacities for fear and anger--for fight and flight--form a positive organ to be used, not a malfunction. This no more commits us to misusing it than our having feet commits us to kicking people.