Infant development: Birth to 3 months Infant development begins at birth. Consider major infant development milestones from birth to 3 months — and know what to do when something's not right. Different words are used for a baby at different stages of growth. These words are not used in the same way by everyone. For example, the word infant may be used until a baby can walk, or only until the baby is one year old. A baby from birth to about 3 months old is sometimes called a newborn. Separated from his mother when he was just an infant, the boy grew up in a children's home. She isn't able to look after herself at all - she's as helpless as an infant. As a parent you give your children a good start in life—you nurture, protect, and guide them. Learn about developmental milestones, including emotional and social development, for babies from birth to 1 year of age. There are many things you can do to help your baby stay safe and healthy. The term infant usually refers to a baby from birth to around 1 year of age. You may also use the term “baby” during this time or “newborn” for little ones up to around 3 months of age. Merriam-Webster defines an infant as a child in the first period of life but doesn't give any age specifics. It describes a baby as an extremely young child. In common terminology, a baby is the very young offspring of adult human beings, while infant (from Latin īnfāns 'baby, child', literally 'unspeaking') [1] is a formal or specialised synonym. The terms may also be used to refer to juveniles of other organisms. The meaning of INFANT is a child in the first period of life. How to use infant in a sentence. Infant cognitive development occurs in the Sensorimotor stage which starts at birth and extends until the infant is about 2 years of age. The sensorimotor stage is made up of six sub-stages. Infants primarily interact with the world through reflexes, such as sucking, grasping, and looking. The eldest of the comers, a girl who wore a triangular shawl, its corners draggling on the stubble, carried in her arms what at first sight seemed to be a doll, but proved to be an infant in long clothes.