There is increasing evidence to show that compassion and altruism are highly beneficial when cultivated from an early age. In the present study we explore the benefits of an intervention programme that seeks to develop affective empathy, compassion and altruism in 9-year-old children from a school of Buenos Aires, Argentina. A pretest-posttest controlled study was carried out with 48 children, half of whom carried out the intervention. The remaining children, who constituted the waitlist group, participated in academic tutoring activities conducted by the same research team. The intervention was successful in promoting children's altruistic and compassionate attitudes, evidenced by the results obtained in the universal altruism test, social integration, and affective response. Effect sizes ranged from medium to large in the intervention group. These positive findings were not observed in the waitlist group (non-significant effect sizes). This study shows that children's self-awareness and awareness of others tend to foster compassion and affective empathy, contributing to individual and collective well-being.