Thabit al-Bannani reported that Anas ibn Malik walked by some children and greeted them. He said, "The Prophet, may Allah bless him and grant him peace, used to do that."  

أَنَّهُ مَرَّ عَلَى صِبْيَانٍ فَسَلَّمَ عَلَيْهِمْ وَقَالَ كَانَ النَّبِيُّ ﷺ يَفْعَلُهُ بِهِمْ  

'Anbas said, "I saw Ibn 'Umar greet children in the schools."  

عَنْ عَنْبَسَةَ قَالَ رَأَيْتُ ابْنَ عُمَرَ يُسَلِّمُ عَلَى الصِّبْيَانِ فِي الْكُتَّابِ