What type of aggression is okay for a 6-year-old boy to show among playmates (e.g. playing bad guys and good guys on the playground and tugging on kids' arms or making threatening gestures with sticks), and should a parent step in to stop it or act in some other way?It's important to recognize that there's a difference between pretending to be aggressive (as when playing good guys and bad guys) and actually being aggressive (as when threatening another child when it isn't in play. I think you can allow more leeway in play than in actual interpersonal behaviour. A child who is threatened by another child pretending to be a "bad guy" won't really be scared or hurt (providing the "bad guy" doesn't really hit him).I don't think it's possible to avoid good guy-bad guy play with little boys. They will do it anyway, no matter what toys they are given or denied. However, you will find there's less "good guy-bad guy" play if your child watches less TV or plays less video games with this theme. It's important to teach our kids that no one is fully a good guy or a bad guy. This may confuse them at first, but over time it's an important lesson to learn.When a child is actually aggressive he is often just protecting his personal boundaries. Animals set their interpersonal boundaries through growls and snarls. An animal is vicious if it actually bites, not if it just warns someone with its voice. Yet we expect our children not to do this. I think a certain amount of growling and snarling is okay from children. They need permission to be able to tell other kids to back off and leave them alone.Real aggression often comes out when a child is angry and doesn't know how to express it and to set a boundary with another child. For example, one child may "bug" and provoke another until the other child lashes out. It's important to teach your child to use words to express what he feels or wants: "Don't touch my stuff," "Don't make faces at me," and so on. We need to coach our children in ways of verbally expressing themselves so they don't need to resort to physical threat and violence.It isn't enough for a child who is being provoked to make wimpy statements like "Please don't do that," or "That hurts my feelings." These just invite further bugging or bullying. A child needs to be able to give the verbal equivalent of a growl or a snarl. This can be done without damaging anyone's self-esteem.What's not okay? Threatening with weapons (other than in what is clearly play). Physically assaulting another child when he hasn't attacked you physically. Remember that physical assaults like kicking, biting, pinching and hitting often happen when the child has overwhelming feelings and doesn't know what to say. Giving your child some strong words to use can prevent him actually attacking someone's body.What about physical retaliation if someone does attack you? I think this needs to be kept as an option kids need to be able to defend themselves. Martial arts training can help a child know when this is necessary, and how to do it in a way that doesn't injure anyone.