The Prophet ﷺ greeted even small children with salām. Anas said: he ﷺ passed by some boys and greeted them. (al-Bukhārī & Muslim). It teaches them their worth and raises them upon good manners.

العربية: عن أنس رضي الله عنه أنّه كان يمشي مع رسول الله ﷺ «فمرّ بصبيانٍ فسلّم عليهم». (البخاري ومسلم).

Greet children with salām — it honours them and teaches them the Sunnah early.