According to the kids shoe size by age chart, the average shoe size for a four-year-old is US 11, which equals a foot length of 6 7/8 inches. However, its important to keep in mind that young children tend to grow at very individual rates, so its always recommended to measure their foot when possible to ensure you choose the right size shoe for their particular needs. Additionally, different brands and styles of shoes may fit differently, so its a good idea to try on shoes before purchasing them to ensure a proper fit.