A baby blessing is an ordinance or sacred act performed by a man who holds the Melchizedek priesthood in the Church of Jesus Christ of Latter-Day Saints (Mormon church). In most cases, the baby’s father performs the blessing as long as he holds the priesthood and is worthy to bless the baby. The purposes of a baby blessing are to name and bless the infant; a baby blessing is not a baptismal ceremony.
There are specific requirements for naming and blessing children. The father giving the blessing and any other invited priesthood holders (often family and friends) form a circle and hold the infant in the center. The father then gives the baby a name and blesses the child. Now the child is officially a member of the Church of Jesus Christ of Latter-Day Saints. The name the baby is blessed with is the name he will be known by on the church records.
During the blessing, the father bestows certain blessings on the infant. Baby blessings are different for each child because the Holy Spirit directs the father on what to say. In general though, most babies are blessed with good health, a strong mind, good judgment, a strong testimony of the gospel, to be a good example to others, to be happy, to be obedient,to have righteous desires, to be baptized, to get married in the temple, to serve others, etc.
Generally, a baby is blessed within the first few months after being born. The baby wears white: girls in blessing dresses or blessing gowns and boys in blessing suits or blessing rompers. A baby blessing is a sacred and joyous event for the family and oftentimes extended family and friends will travel to be a part of the momentous occasion. Source:
http://blessinggowns.storeblogs.com/2010/06/01/what-is-an-lds-baby-blessing