Baarakallaahu laka fil-mawhoobi laka, wa shakartal-waahiba, wa balagha 'ashuddahu, wa ruzigta birrahu. The reply of the person being congratulated is to say: Baarakallahu laka wa baaraka 'alayka, wa jazaakallaahu khayran, wa razaqakallaahu mithlahu, wa 'ajzala thawaabaka
Meaning: 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. The reply of the person being congratulated is to say: May Allah bless you, and shower His blessings upon you, and may Allah reward you well and bestow upon you its like and reward you abundantly
Source: Hisn al-Muslim (Fortress of the Muslim) — Saʿīd ibn ʿAlī al-Qaḥṭānī (Congratulations for new parents and how they should respond)
How to seek Allah's protection for children
Children
كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُعَوِّذُ الحَسَنَ وَالحُسَينَ رضي الله عنهما ((أُعِيذُكُمَا بِكَلِمَاتِ اللَّهِ التَّامَّةِ مِنْ كُلِّ شَيْطَانٍ وَهَامَّةٍ، وَمِنْ كُلِّ عَيْنٍ لاَمَّةٍ))
Ibn 'abbas related that the Messenger of Allah used to commend Al-Hasan and Al-Husayn to Allah’s protection, saying:(O'eethukuma bikalimatil-lahit-tammah, min kulli shaytanin wahammah, wamin kulli 'aynin lammah.)
Meaning: Ibn AAabbas related that the Messenger of Allah used to commend Al-Hasan and Al-Husayn to Allah’s protection, saying:(I commend you two to the protection of Allah’s perfect words from every devil, vermin, and every evil eye.)
Source: Hisn al-Muslim (Fortress of the Muslim) — Saʿīd ibn ʿAlī al-Qaḥṭānī (How to seek Allah's protection for children)
Hunalika da'a zakariyya rabbahu qala rabbi hab lee min ladunka thurriyyatan tayyibatan innaka samee'u alddu'ai
Meaning: At that, Zechariah called upon his Lord, saying, "My Lord, grant me from Yourself a good offspring. Indeed, You are the Hearer of supplication."
Source: The Noble Qur'an (Saheeh International) (Qur'an 3:38)