Answer: On this site, the word baby means any child from birth to age 4. Newborn refers to babies under three months of age. Infants are babies from three months to one year old.Toddlers are babies from one year to four years of age.nswer: On this site, the word baby means any child from birth to age 4. Newborn refers to babies under three months of age. Infants are babies from three months to one year old.