Violence is a major public health problem globally, with the highest rates in low- and middle-income countries (LMICs) in the Americas and southern Africa. Parenting programmes in high-income countries can diminish risk for violence, by reducing risk factors such as child aggression and harsh parenting, and increasing protective factors such as child cognitive development and school readiness. However, there is critical need to identify low-cost programmes with replicable benefits that work in real-world LMICs contexts. A three-arm, randomised, single-blind trial evaluated effects of two low-cost, group-based parenting programmes recommended for LMICs (ACT: Raising Safe Kids; DBS: dialogic book-sharing) on child aggression (primary outcome), child development, parenting, maltreatment, and stress. Participants were 369 children with medium-high levels of aggression (mean age 3.1 years at baseline) in poor households. Interventions were implemented in city health and education services in southern Brazil. Maternal reports, filmed observations, child tasks, and hair cortisol were assessed at baseline, 1-month post-intervention, and 8-month follow-up. Intention-to-treat analyses compared each of ACT and DBS with a control group. Three hundred sixty-eight (99.7%) participants completed follow-up assessments 8 months after the interventions. There was no effect of ACT (standardised mean difference, SMD 0.11, 95% CI - 0.05, 0.27) or DBS (SMD 0.05, 95% CI - 0.11, 0.21) on the primary outcome of child aggression. ACT reduced harsh parenting behaviour post-intervention (SMD - 0.23; 95% CI - 0.46, 0.01), but not at follow-up. DBS improved book-sharing practices at both time points (e.g., maternal sensitivity at follow-up SMD 0.33; 95% CI 0.08, 0.57). There were no benefits of either programme for other parenting, child development, or stress outcomes. Two parenting programmes in Brazil had small effects on parenting practices but did not reduce child aggression or several other important risk/protective factors for violence. Effective early interventions that reduce violence in real-world LMIC settings are highly desirable but may be challenging to achieve.