Tank tops tend to fit for longer as there are no sleeves to worry about, so the sizing is quite flexible - you'll find your child will get a lot of wear from this! We find we use it a lot on our baby under a jumper (and over a vest or t-shirt) in winter, for an extra layer of warmth.
Age 0 to 9 months: 30cm long by 26cm wide
Age 1 to 2 years: 34cm long by 27.5cm wide
Age 2 to 3 years: 40cm long by 30cm wide
Age 4 to 5 years: 44cm long by 34cm wide
Machine washable at 30 degrees on the wool cycle, or hand wash. Do not tumble dry.