Du'a for children's success and long life

اللَّهُمَّ يَسِّرْ أَمْرَهُمْ، وَوَفِّقْهُمْ فِي حَيَاتِهِمْ، اللَّهُمَّ أَمْدِدْ فِي عُمْرِهِمْ بِالصِّحَّةِ وَالْعَافِيَةِ فِي طَاعَتِكَ وَرِضَاكَ

Allahumma yassir amrahum, wa waffiqhum fi hayatihim, Allahumma amdid fi 'umrihim bis-sihhati wal-'afiyati fi ta'atika wa ridak

O Allah, ease their affairs and grant them success in their lives. O Allah, extend their lives with health and well-being in Your obedience and pleasure.

A general supplication, not a narration from the Prophet (peace be upon him).