When should you worry about aggressive behaviour in children?

What the evidence says

Aggression such as hitting, biting or throwing tantrums is extremely common in toddlers and preschoolers. Canadian paediatric guidance notes that some noncompliance, tantrums and aggression between ages 2 and 5 are normal and usually fade as children mature, with aggression typically peaking around age 3. The same guidance also notes that behaviour considered normal at age three may be a sign of a real problem at age five, so context and age matter.

What tips it from 'normal phase' into 'worth a closer look' is not the aggression itself but its pattern. Canadian sources point to frequency, intensity and duration that are out of step for the child's age, especially when the behaviour causes real distress or gets in the way of daily functioning at home, daycare or school. The CDC frames it similarly: a behaviour disorder becomes more likely when defiance or aggression is unusual for the child's age, persists over time, or is severe rather than an occasional outburst.

Specific things to flag for your doctor include: aggression lasting more than a few weeks despite consistent limit-setting, injuries to the child or others, cruelty to animals, fire-setting, use of weapons, or threats to seriously hurt someone. American child psychiatry guidance stresses that violent behaviour in a child of any age should be taken seriously rather than assumed to be 'just a phase.' It's also worth knowing that aggression is sometimes the visible tip of something else entirely, such as anxiety, ADHD, a language or sensory processing difficulty, or a mood disorder, so a doctor may look beyond the behaviour itself. If you're concerned, your family doctor or pediatrician is the right first stop.

They can screen for underlying conditions and, if needed, refer to a psychologist, developmental pediatrician or child psychiatrist for a full assessment.