How can a child's nervousness and bad temper be treated?

To control anger, one can seek refuge in Allah from the accursed Shaytan, remain silent, change one's posture (sit down or lie down), remember the reward for suppressing anger and the Paradise for those who do not get angry, know the guidance of the Prophet, peace and blessings be upon him, and that suppressing anger is one of the signs of the righteous, reflect on the disadvantages of anger, and make supplication. The story of the boy and the nails illustrates that angry words leave deep and hurtful scars in the souls of others that do not disappear even with an apology.