The difference between a kid and a little kid is that a kid is considered to be a kid in the age range of 9 years old to 12 years old.
While a little kid is a kid that is age 8 to 4 years old however a 4 year old is sometimes thought of as a toddler as ages 1 to 4 is considered to be a toddler and a baby is considered to be 1 year old and under.
When a kid is considered a little kid the little kid is between the ages of 4 years old to 8 years old.
So if your 8 years old to 4 years old then you'd be a little kid until you turned 9 years old.
A kid is considered to be age 9 years old to 10 years old.
A big kid would be a kid of ages 10 years 11 years old to 12 years old and then after 12 years old when you become 13 years old you would be a tween.
However a 13 year old could also be considered a teenager as teen is in the name but most people don't consider someone a teenager until 15 to 16 years old.
When you reach 18 then you're an adult legally but there's still teen in the age.