Over half a million children between 0 and 5 years of age in Colombia have been affected by a civil conflict that has spanned over six decades. Exposure to violence during early childhood, or being born to a household that has been formerly victimized, may have devastating consequences on early childhood cognitive and socio-emotional development. In doing so, violence can compromise the right to lead healthy and productive lives for thousands of children in Colombia.

First, violence leaves a legacy of poverty and psychological trauma (Ibañez \& Moya, 2010; Moya, 2018). Children who experienced violence during early childhood lag in cognitive, social, and emotional development, while exposure to violence increases the probability of child neglect (Harker, Moya, \& Riveros, 2015; Cuartas, Harker, \& Moya, 2015). Protecting children from effects of violence, toxic stress, and deficits in family care is therefore one of the key challenges as Colombia transitions into a post-conflict stage and for the construction of a more equal and peaceful society. More generally, identifying cost effective ways to protect children and children from the effects of violence, toxic stress, and deficits in maternal care is a key challenge in contexts of violence and humanitarian crises.

Recent evidence exploring the effect of interventions to promote positive child-development suggest a promising path through the attention to their caregivers (Singla Kumbakumba, \& Aboud, 2015; Rahman et al., 2013). Building from this evidence, in this trial the researchers will evaluate the effectiveness of a group-based psychosocial program (Semillas de Apego) for victimized caregivers with children 2 to 5 in Colombia, a country devastated by violence. The program promotes healthy child-parent attachments as a pathway for a proper development among children exposed to violence. By fostering caregivers' mental health and their capacity to become a source of emotional protection, the intervention helps children reach their full potential amid such traumatic circumstances. Delivered in a 15-week curriculum, Semillas de Apego first provides tools so that victimized caregivers can start processing their own trauma. Then, the program focuses on allowing a proper understanding of the child's development trajectories and how they affected by the experience of adversities (such as violence exposure). Finally, the curriculum works towards fostering positive child-rearing practices. Taken together, Semillas de Apego's curriculum aims to foster the healthy child-parent attachments that promote appropriate affect regulation and healthy emotional development in the midst of adverse circumstances.

The current trial focuses on the effectiveness evaluation of Semillas de Apego in Tumaco, a municipality in Colombia heavily affected by violence and poverty. Over a time-span of 23 months, the researchers will follow the implementation of Semillas de Apego with 40 groups of 16 participants each, all of them mothers or primary caregivers of children 2 to 5. This will allow the researchers to reach a total of 640 participants and their children. The impact evaluation will be based on a cluster- randomized control trial in which 1280 eligible subjects, nested within 18 child development centers, will be assigned to either an intervention arm or a control group. The former group will participate in 15 group-led session over the period of 3 months; the latter will continue to have access to the regular early childhood programs offered through the centers to which children are affiliated. Data will be collected at baseline and two follow-ups: 1 and 12 months after the implementation has concluded. The researchers hypothesize that the program will have a positive and sequential impact on the following dimensions: (i) primary caregiver's mental health, (ii) child rearing practices, (iii) quality of child-parent emotional bond, (iv) children's mental health, and (v) children's cognitive and socioemotional development.