Despite the multitude of negative outcomes associated with thin-ideal internalization for girls and women living in westernized societies, we know very little about how early in development thin-ideal internalization occurs or how it might manifest in very young children. This cross-sectional investigation assessed body size stereotyping and thin-ideal internalization in 55 preschool girls (ages 3–5 years) from the Southwestern U.S. using a new method of assessment that is more sensitive to the cognitive developmental stage of this age group. Results suggest that girls as young as 3 years old are already emotionally invested in the thin ideal. Discussion considers moving beyond the demonstration of fat stigmatization per se to measure how personally invested preschool children may be in beauty ideals.