Kids rings are mostly available in size 1/2 – 4 1/2 (12mm up to 15.3mm). To measure the ring size:

• Take a piece of string (not thread as it tends to extend) and wrap it around the child’s finger. Make sure the string is not too tight or loose.
• Cut the string and measure it with a millimeter ruler. The measurement obtained is the inside diameter of the ring.

In most cases, a 1/2 size ring is for infants, size 1 and 2 for toddlers (1-4years), size 2 1/2 is for 3-6 years and so on.