Du'a for children's best manners

اللَّهُمَّ اهْدِهِمْ لِأَحْسَنِ الْأَخْلَاقِ، لَا يَهْدِي لِأَحْسَنِهَا إِلَّا أَنْتَ، وَاصْرِفْ عَنْهُمْ سَيِّئَهَا، لَا يَصْرِفُ عَنْهُمْ سَيِّئَهَا إِلَّا أَنْتَ

Allahummah-dihim li'ahsanil-akhlaq, la yahdi li'ahsaniha illa ant, wasrif 'anhum sayyi'aha, la yasrifu 'anhum sayyi'aha illa ant

O Allah, guide them to the best of manners, for none guides to the best of them except You. And turn away from them evil manners, for none turns them away except You.

Adapted into the plural for children from Ṣaḥīḥ Muslim 771a.