The chord symbol iii could be followed by the letter a to indicate that it is F# minor chord in root position (ie not inverted) - D major scale chord iiia. Instead, iii could be followed by the letter b to indicate that it is F# minor chord in 1st inversion - D major scale chord iiib.
According to the Centers for Disease Control and Prevention, a baby is considered an infant until he reaches one year of age. During this stage, the infant reaches several developmental milestones.
Infant is a more formal term for a baby, the youngest category of child. A child is no longer considered an infant when able to walk and talk, which, in most cases, is at about 1 year. The term child covers the age range from birth to puberty.