Preschool children infer each other's emotional state, such as joy, anger and sadness, by observing and understanding each other's facial expressions. It is a very important ability to understand each other's emotions, feel each other's needs and communicate socially. Studies have shown that children can recognize facial expressions at an early age, and this ability will continue to develop and improve with age. Parents and educators can help children develop this ability and promote social interaction and emotional cognition by providing more facial expression information and training.