This activity is for newborns until three years old (and beyond insha'Allah). The importance of reciting the athkar an-nawm cannot be overstated. Even at birth the foundation for language is being laid so reading the athkar nightly has this added benefit and Islamically, is something not be neglected insha'Allah.
Some nights you may be tired (or perhaps exhausted is more accurate) but do your best not to forgo this important activity that benefits your child in dunya and in akhira...may Allah reward you.
Here are the athkar to be recited and there is a link at the end that provides more information (unfortunately, it is only in Arabic but I'm working on finding something in English too insha'Allah). Jazakillahu Khayr to my co-blogger for locating this information!
عَنْ ابْنِ عَبَّاسٍ رَضِيَ اللَّهُ عَنْهُمَا قَالَ : ( كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُعَوِّذُ الْحَسَنَ وَالْحُسَيْنَ وَيَقُولُ : إِنَّ أَبَاكُمَا كَانَ يُعَوِّذُ بِهَا إِسْمَاعِيلَ وَإِسْحَاقَ : أَعُوذُ بِكَلِمَاتِ اللَّهِ التَّامَّةِ ، مِنْ كُلِّ شَيْطَانٍ وَهَامَّةٍ ، وَمِنْ كُلِّ عَيْنٍ لاَمَّةٍ ) رواه البخاري (3371)
Ibn 'Abbaas (radhi-yAllaahu 'anhumaa) related that the Messenger of Allaah (sal-Allaahu 'alayhe wa sallam) used to commend al-Hasan and al-Husayn to Allaah’s protection, saying:‘I commend you two to the protection of Allaah’s perfect words from every devil, vermin, and every evil eye.’ (U'eethukumaa bi kalimaat illahi al-taammah min kulli shaytaanin wa haammah wa min kulli 'aynin laammah).
You can also read the mu3awathaat (surat al-ikhlas, al-falaq, and an-nas) and blow in your palms and wipe over your child's/childrens' bodies.
Here is a fatwa for further reference but again, unfortunately it's only available in Arabic : Fatwa from Islam-qa.com