"Child Related Definitions" (Just for interest) ... 

Legally, in the United States, a child is anyone under the age of 18. However, for the purpose of information we are going to break down most of the terms here associated with Babies and Children. *There are no hard and fast rules to be certain and some terms refer to ability more than actual age so use the definitions here as a Guideline of course.

0-28 days/ 0-3 months
Newborn: Sometimes referred to as the "4th trimester", (the first three taking place within the womb during pregnancy) and other times just the 1st month only. In developed countries, the average birth weight of a full-term newborn is anywhere between 6lbs and 10lbs (2.7-4.6 kg).

1-12 months
Baby: Usually used to refer to a little one from birth up until they can walk.
Infant: (from the Latin word infans, meaning "unable to speak" or "speechless") is the more formal term for Baby.

1-3 years
Toddler: a baby turns into a toddler when they can "toddle", i.e. walk shakily. This usually happens around 1 year but may occur earlier or later depending on development.

4-10 years/ 0-18 years (legal)
Child/ Kid: This is the broadest, most general word out of this list.  Newborns, babies, infants and toddlers are all children. The legal age range is from 0-18 years old. Colloquially though, a "child" is aged from around 4 years old up to around 10 years old.

3-5 years
Pre-Schooler: The first year of preschool education is also referred to as Nursery school while the second year is often called Kinder garden. (About one million children ernroll in the first year and approximately 3.4 million enroll in the second.)

6-12 years
Grade-Schooler: U.S. children enter formal schooling around age 6. (This can be earlier or later based on their birth date relative to the school calendar.) On average, 3.7 million children enter the first year of grade school, each year.

11-12 years
Adolescent:  Adolescence is known as the transition time frame between childhood and adulthood. This period also coincides with the onset of puberty.
Pre-Teen: Generally recognized as a child just below the age of 13.

13-19 years
Teenager: Widely accepted age range between 13 and 19 based on the simple occurrence of the word "teen" in the age pronunciation and spelling.

12-24 years
Youth: Another broad term which the dictionary describes as the period between childhood and maturity, especially adolescence and early adulthood.