Mood disorders 

First, are there mood issues? Kids who are bipolar, in their manic stages, very frequently become aggressive. They lose self-control, they become impulsive. On the other end of the spectrum, when they become depressed, although aggression is less common, they can become irritable, and sometimes that irritability and cantankerousness causes kids to lash out.

​

Psychosis 

The psychotic illnesses may also manifest with aggression. For example, kids with schizophrenia are often responding to internal stimuli that can become disturbing. Sometimes kids with schizophrenia become mistrustful or suspicious, or full-blown paranoid and they wind up striking out because of their own fear.

​

Frustration 

Kids who have problems with cognition (what’s now called intellectual impairment) or communication (including autism) may also manifest with aggression. When children with these conditions become aggressive, they often do so because they have difficulty dealing with their anxiety or frustration and can’t verbalize their feelings as others do.

 

The aggression may also be a form of impulsivity.

 

Impulsivity 

There are the disruptive behavior disorders. In children with ADHD, the most common of them, impulsivity and poor decision-making can lead to behavior that’s interpreted as aggressive. These children often don’t consider the consequences of their actions, which may come across as callous or malicious when they are really just not thinking.

​

Conduct Disorder 

With conduct disorder, aggressiveness is part of the matrix of the illness, a large component of what that is. Unlike the child who just isn’t considering consequences of his actions, kids with CD are intentionally malicious, and the treatment and prognosis are quite different.

​

Injury

Sometimes there are organic reasons for aggressive outbursts, when a child has frontal lobe damage or certain types of epilepsy. In these cases there may be no comprehensible reason for the aggressive episode, and the episode could have an explosive component.

​

Trauma

Finally, there are times when aggression in children or teenagers is provoked by stressors in their situation, and do not represent an underlying emotional illness. But it is important to understand that this is fairly rare, and when aggression begins to happen on a more frequent basis, it could represent a brewing emotional problem.

​

https://childmind.org/article/aggression-in-children-causes/