It is narrated on the authority of Husain (RA) that he went to teach a man how to give greetings and said, You will say:

بَارَكَ اللَّهُ لَكَ فِي الْمَوْهُوبِ لَكَ وَشَكَرْتَ الْوَاهِبَ وَبَلَغَ أَشُدَّهُ وَرُزِقْتَ بِرَّهُ

BaarakAllahu laka fil-mawhoobi laka, wa shakartal-waahiba, wa balagha 'ashuddahu, wa ruziqta birrahu.

May Allah bless you with His gift to you, and may you (the new parent) give thanks (to Allah - the giver), may the child reach the maturity of years, and may you be granted its righteousness.

Reference: Sahih (Albani). Abu Dawood: 441