Background: Despite evidence on their short-term effectiveness, the long-term effects of group-based parenting interventions are unclear, programs are hard to scale up, and effects on parents of infants and toddlers are mixed. Objective: We evaluate the impact of a parenting intervention, "Crianza Positiva," that combines 8 group sessions with a 6 months e-messaging component. The program targets parents of infants and toddlers, is designed to be scalable by using low-cost delivery formats and a structured framework, and relies on a "top up" module to sustain the effects. Methods: We analyze video-recordings of a free play activity to rate the quality of child-caregiver interaction. We compare outcomes across three arms: (a) workshop + messages, (b) workshop only, and (c) a weekly unstructured playgroup. Because assignment to treatment is not random, we use inverse probability weighting to address initial unbalances and differential attrition. Our sample includes 442 disadvantaged families with infants/toddlers enrolled in early childhood centers in Uruguay. Results: Results show significant and sustained benefits of the program on child-caregiver interaction quality, with medium effect sizes in the affective (d = 0.44) and teaching dimensions (d = 0.59). Conclusions: The data suggest that group parenting interventions may help improve the childrearing environment among parents of children aged 0-2. Due to its protocolized design and the low cost of integrating it into early-childhood centers, the program has a potential for widespread implementation. Still, definitive conclusions are precluded by the evaluation design. Future randomized designs are needed.