In Jyotish tradition, six nakshatras at the junctions of water and fire signs are known as Gand Mool nakshatras: Ashwini, Ashlesha, Magha, Jyeshtha, Moola and Revati. When a child is born in one of these, many families perform a Gand Mool Shanti Puja.
The puja is usually done when the same nakshatra returns, about 27 days after birth. It includes Ganesh puja, worship of the nakshatra devata, Navagraha puja, mantra jaap for the relevant nakshatra and a havan, often with the family and the baby present for part of the ritual.
If the shanti could not be done at that time, families often perform it later on a suitable muhurat. The Pandit will look at the birth details and advise on timing and vidhi.