Background: The research carried out in the last years outlined that childbirth could be considered as a sufficient stressor for the insurgence of posttraumatic stress (PTS) symptoms with important consequences for the child care. Objectives: In a longitudinal perspective, this study focused on PTS symptoms after childbirth to understand their impact on maternal parenting stress and children's adjustment. First, we investigated whether childbirth-related PTS symptoms, at 87 h and 3 months postpartum, were associated with parenting stress and children's adjustment at 18 months. Second, we explored, at 18 months, the predictive effects of postpartum PTS symptoms on children's adjustment and verified the mediational effect of parenting stress this association. Methods: Eighty-eight women participated and completed the following questionnaires: PPQ (for assessing maternal PTS symptoms at 87 h, 3 and 18 months postpartum), PSI-SF (for maternal parenting stress at 18 months) and CBCL (for children's adjustment at 18 months). Results: Findings outlined that more PTS symptoms at 3 months are associated with greater levels of parental distress and they predicted children's adjustment at 18 months. Moreover, maternal parenting stress explained the predictive effects of childbirth-related PTS symptoms on children's adjustment. More precisely parental distress partially mediated the association between PTS symptoms and children's internalizing behaviors, while the perception of the difficult child fully mediated the effects of PTS symptoms on externalizing behaviors. Conclusion: This study was consistent with the idea that women may experience childbirth-related chronic distress and child adjustment was connected to different sources of parenting stress.