Anas (May Allah be pleased with him) passed by some children and greeted them (by saying As-salamu 'alaikum to them). Then he said:
The Prophet ﷺ used to do the same.

[Al-Bukhari and Muslim].

وعن أنس رضي الله عنه أنه مر على صبيان فسلم عليهم وقال: كان النبي ﷺ يفعله. ((متفق عليه))