This also applies if you are a small, junior or petite size in womens clothing. Sometimes it can be less expensive to buy large or Xlg clothing in the children's section. :
Ugg Boots Sizing Chart - Uggs Sizing Information
UGG Boots, Shoes & More for Kids & Toddlers - Bloomingdale's
UGG® Neumel II Chukka Boot - Little Kid / Big Kid - Chestnut | Journeys
UGG Australia Classic Tall II Big Kids Boots Size 6 - Walmart.com