This study examined the associations between maternal stress, postpartum depressive symptoms, breastfeeding success, parenting behavior, and maternal perceptions of the newborn in the early postpartum period. A descriptive, correlational design was conducted with 252 mothers recruited from a postpartum ward in Central Anatolia, Türkiye, between May 2024 and May 2025. Postpartum depression was identified in 11.5% ( n = 29) of participants. At the nominal level, some variables appeared to be associated with study outcomes. However, after adjusting for multiple comparisons using the Benjamini–Hochberg false discovery rate (FDR) procedure, none of these associations remained statistically significant (all adjusted p > 0.05). Accordingly, no significant differences were observed between maternal characteristics and breastfeeding success, parenting behavior, or newborn perception after controlling for multiple testing. Regression analyses indicated that maternal stress and postpartum depression were not significant predictors of breastfeeding success or newborn perception. In contrast, parenting behavior was negatively associated with maternal stress. Further analysis showed that both maternal stress (B = −0.046, p < 0.001) and postpartum depression (B = −0.042, p = 0.011) were significant negative predictors of parenting behavior (F = 11.735, p < 0.001; R2 = 0.086). Moderation analysis further revealed that postpartum depression moderated the relationship between maternal stress and parenting behavior, with the negative impact of stress being stronger among mothers with higher depressive symptoms. These findings highlight the importance of maternal psychological well-being in shaping parenting behavior during the early postpartum period, underscoring the need for routine screening for stress and depression to support healthy parenting.