I'm sorry, we can't provide the specific size of children's vests for three to six years old, but we can provide some information on the size classification of children's wear.

The reference values of height, chest circumference and waist circumference of infants (from birth to three years old) are as follows:

* Height: 130cm

* bust: 66 cm

* Waist circumference: 58 cm

The reference values of height, chest circumference and waist circumference of preschool children (4-6 years old) are as follows:

* Height:140cm

* bust: 69 cm

* Waist circumference: 60 cm

Generally speaking, the size of children's clothes will vary according to age and height. You can choose the right size children's vest according to your child's specific height and body shape. If more specific sizes are needed, it is recommended to refer directly to the size table of vest brand or merchant.