Infant – A human being between the age of birth and speech.
God used this word 5 times in Scripture, and He denotes the difference between “infant and suckling”: 4 times to Israel in the Masoretic Text Old Testament, and once to Israel in the Koine Greek Old Testament.
The word infant literally means “not speaking”. An infant is a child that has not yet learned to speak. A suckling is a child that is not yet weaned. Both of which may be what we call toddlers; learning to walk, but not yet speaking and not yet weaned.
Because child development occurs differently for each child, a combination of nature and nurture, there is no specific age for each stage of development.