In the right ear of the new-born baby, the Adhan may be recited, and in the left ear, the iqamah this is done immediately after the baby is bathed.
On the birth of Sayyidna Hasan to Sayyidah Fatimah (Radhiallaho Anha) the Noble Prophet,(Sallallaho alaihe Wasallam) had said the Adhan in his ear. (Abu Dawood and Tirmizi.) This practice ensures safety to the child from epilepsy.
Hafiz ibn Qiyyim (Radhiallaho Anho)says
the significance of saying the Adhan and the iqamah in the ears of the child is that the first words he hears declare the greatness and majesty of Allah.
The words of testimony are those which a man recites on embracing Islam. In other words, this is a pronouncement of the creed of Islam. Besides, at the sound of Adhan and iqamah, Satan distances himself. At this early age, the child is thus invited to Allah the Majestic, to Islam and to the worship of Allah. This call forestalls temptation by Satan and ensures an unblemished faith. Moreover, it is a forearming against Satan and temptation.