Infant caregiving tasks involve frequent bending and lifting, which may cause or exacerbate pain in an already susceptible postpartum population. The biomechanics of daily infant lifting tasks in mothers has never been characterized but could inform childcare ergonomic guidelines and training to reduce the risk of musculoskeletal injuries among caregivers. In this prospective biomechanics study, 11 healthy mothers lifted their own 15-week old infants in three ways:​ picking infant off the floor, from a diaper changing table, and within an infant car seat placed on the floor. Mechanics were compared using one-way multivariate analysis of variance. Participants identified mild levels of stress, anxiety and depression, and pelvic floor muscle and back pain symptoms consistent with postpartum recovery. Mothers exhibited greatest sagittal knee and trunk, and greatest 3D hip angles and power generation during the floor task, suggesting that this was more demanding and required a consistent deep squat lifting strategy. Lifting infants within a car seat added ∼4 kg mass, which elicited similar hip sagittal kinetics and greater muscle activity but reduced knee and trunk motion due to the elevated handle height and variability between mothers’ lifting patterns. The changing table task was the least demanding, with lowest lower extremity mechanics, as mothers asymmetrically sidebent and rotated their trunk to lift baby, which has implications for ergonomics. This ecological study highlights biomechanical challenges of infant lifting and the importance of ergonomic awareness in everyday caregiving. Understanding task-specific lifting mechanics can inform interventions that support caregiver well-being while ensuring infant safety.