Leg groin pain behind the knees may be caused by various factors, including muscle strain, arthritis, or injuries. It is recommended to pay more attention to keeping warm and resting during the postpartum period, and to observe for any abnormalities. If it occurs when the child is older, it is advisable to visit a regular hospital for a check-up to determine if there are any unusual conditions. Additionally, maintaining a positive mood, regular lifestyle, balanced nutrition, and proper care can help alleviate the pain.