بَارَكَ اللَّهُ لَكَ فِي الْمَوْهُوْبِ 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, may the child reach the maturity of years, and may you be granted its righteousness.

Reference: This is menioned as a saying of Hasan Al basri Rahimullah. See tuhfatul maodud fi Ibn Qaiiyum, Page. 20