Tag reads "This garment is thermal underwear and is intended for use as underwear not sleepwear."

Labeled a size 4, but fits like a modern 2T

Measurements - 

Armpit to armpit: 9" laid flat or 18" circumference
Waist: 18" circumference

Length: 11" shoulder to bottom hem

Sleeve length: 11.5" 

100% polyester - material is very stretchy

A4