Anas (May Allah be pleased with him) reported that he passed by some children and greeted them. Then he said: "Messenger of Allah (PBUH) used to do the same.''
[Al-Bukhari and Muslim].

Commentary: By greeting children, we please their hearts and also vent our modesty. Besides, the importance of As-Salam is unconsciously felt by them. Above all it is the Sunnah of the Messenger of Allah (PBUH) and so we are supposed to put it into practice.