Should be only low levels until puberty kicks in.

Most of the research into testosterone and aggression comes from adults.

Some small studies have found a link between testosterone levels in children and aggression, particularly in boys, but not all. Similarly some studies have suggested low cortisol in association with aggression, but other studies have found links to high cortisol.

A small study of pre pubertal and pubertal children (boys and girls) found testosterone levels were associated with high moodiness and low attachment. Testosterone was also associated with low sociability, but only in the prepubertal group. 

One study suggested that the influence of these hormones can modulate the balance of aggressive tendencies and empathy, with cortisol being relevant only to boys and testosterone only to girls.

All these studies at high risk of bias.