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. Infancy, among humans, the period of life between birth and the acquisition of language approximately one to two years later. The average newborn infant weighs 3.4 kg (7.5 pounds) and is about 51 cm (20 inches) long. Learn more about infancy in this article. Find health, safety, nutrition, vaccines, and milestones info for babies and toddlers. The meaning of INFANT is a child in the first period of life. How to use infant in a sentence. infant A child between birth and age 1 (or 2). See High-risk infant, Premature infant, Very-low-birth-weight infant. McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc. 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. 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. 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. 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. An infant (from Latin īnfāns 'baby, child', literally 'unspeaking') [1] is a very young human being. Baby is an alternative term for infant. The terms may also be used to refer to juvenile beings of other organisms.