The reason some girls have baby faces is due to hormonal influences during their development. Specifically, high levels of estrogen in growing girls can prevent the growth of facial bones, leading to features like a larger forehead, snub nose, full cheeks, and plump lips. These characteristics are often associated with youthfulness and contribute to a baby-faced appearance.
Additionally, estrogen can increase the thickness of lips and the amount of fat deposited in the cheek area. This further enhances the baby-faced features.
While many people find baby faces attractive, it can also be a source of self-consciousness for some individuals.