What age ranges exactly are toddlers, preschoolers and Kindergarteners?

Generally, 0-12 months would be infant, 1-3 years would be toddler, 3-5 preschooler, 5 years+ would be school-age. I have noticed the word "baby" tends to be more flexible and is often used with any child from infant through preschooler, as a word of deep attachment and responsibility on the parent's part rather than a reference to the child's chronological age. (For example, in a moment of illness, stress, or fear, people will call even their older child their "baby.") In the US there is a wide range of answers to this and different people would not give exactly the same ranges, depending on geography or culture or personal opinion. Can't speak for any other English-speaking countries.

Toddler: 2 & 4

Preschool: 3 & 4

Kindergarten: 5 & 6

0-12 months: infant/baby

12-18 months: young toddler

18-30 months: older toddler

2 1/2 - 4 years: preschooler

5-6 years: kindergartener

In keeping with Piaget's theory of child development, birth to age 7 are consider "early childhood", with "middle childhood" beginning around age 8.

Can't speak for England, or even other Americans, but I would put the ranges at:

0-12 months Infant/baby. (And the first 6-8 weeks or so could also be called newborn.)

1-2 years: Toddler.

2-4 years preschooler.

4 years+ child. (Or the specific grade level could be mentioned if relevant.)