Five randomized controlled trials have shown that child-parent psychotherapy (CPP) improves trauma symptoms in children. Less is known about parent symptoms or moderators of symptom change. In a sample of 199 parent (81% biological mother; 54% Latina/o) and child (aged 2 to 6 years; 52% male; 49% Latina/o) dyads who participated in an open treatment study of CPP, this study investigated whether parent and child symptoms similarly decreased during treatment and whether improvement was moderated by parent, child, and treatment characteristics. Parents completed baseline and posttreatment interviews regarding exposure to traumatic events, posttraumatic stress symptomatology (PTSS), and other mental health indices. Latent difference score analysis showed that PTSS significantly decreased by more than 0.5 SD for parents and children. The PTSS improvement in parents was associated with reductions in child avoidance, r = .19, p = .040, and hyperarousal, r = .33, p < .001. Girls showed a greater reduction than boys in reexperiencing, β = -.13, p = .018, and hyperarousal, β = -.20, p = .001. Contrary to expectations, parent and child improvement in PTSS was greater for those with fewer parental lifetime stressors, β = .15 to .33, and for those who participated in fewer treatment sessions, β = .15 to .21. The extent of improvement in parent PTSS varied based on clinician expertise, β = -.20, p = .009. Significant reductions in parent and child PTSS were observed during community-based treatment, with CPP and symptom improvement varying according to child, parent, and treatment characteristics.