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 - various definitions. Toddler - older. Explanation: In medicine, an infant is a child under 12 months (at least in the UK). However, in UK schools, the 'infant years' are (or used to be - the system is different now from when I was at school!) the period from ages 4 to 7. The child would then progress to junior school (often within the same school) at age 7. 'Toddler', as far as I know, has no definition in medicine and is colloquially used of a child who is big enough to walk but is still considered a baby - 'toddling' is the kind of unsteady walking associated with young children.