A size 6 is generally too small for most 12-year-olds; at that age, children often wear larger youth sizes (like 10-12 or 14-16) or are transitioning into adult sizes (Women's XS/S), depending on their height and build, as size 6 is often for much younger children (around 6-7 years old). Always check the brand's specific size chart and the child's measurements (chest, waist, height) for the best fit.
Size 6X is a true size bigger than size 6 and a true size smaller than size 7 - for the most part *(more on that later). That means a size 6X is about an inch bigger around and about 2" longer in length."
An Australian size 12 is roughly a US size 8, UK size 12, and European size 40, translating to measurements around 97-101cm bust, 78-82cm waist, and 105-109cm hips for women's clothing, often considered a Medium (M). For boys, an AU size 12 fits a 68cm waist and 150cm height, while kids' sizes can vary.
A youth small typically corresponds to sizes 6-7, suitable for children aged 6-7 years, with chest measurements between 25-27 inches.
In the realm of footwear, "GS" stands for Grade School, a sizing term predominantly used by major athletic and lifestyle shoe brands. This category is specifically designed for children, typically ranging from age 8 to around 12 years old. However, what makes GS sizes particularly interesting is their crossover appeal.
The transition from children's to adult sizes usually happens after size 13, which moves into an adult size 1. This shift often comes between ages 8 and 12, though every child is different. Following size 13, the next size is an adult size 1. This system is consistent across the UK, US, and Australian sizing charts.
According to Dyone Cupples, owner of a children's online consignment boutique TheNextSizeUp.com, "Generally a 6x runs slightly larger in width and length than a 6 — it's like a 6 and a half. It seems to fill a gap in sizes where many girls fall."