Scaling up of Brazil's Criança Feliz early childhood development program: an implementation science analysis.

To address inequities that prevent socioeconomically vulnerable young children from reaching their full developmental potential, Brazil implemented Programa Criança Feliz (PCF) ("Happy Child" early childhood development program) in 2934 of its 5570 municipalities. A qualitative case study was carried out on the basis of in-depth interviews with 22 key informants, employing purposive sampling, from past or current national and state coordination teams. Thematic analysis followed the RE-AIM framework, and complex adaptive system constructs mapped how barriers and enablers influenced scale-up. One overarching theme related to PCF emergence, and 18 subthemes were identified within the RE-AIM. An enabling national political environment favored PCF emergence through a top-down approach that led to governance challenges. Changes in the enrollment criteria for families facilitated reach, and evidence-based methodology favored the designing of the home visits. However, operationalizing the intersectoral actions remains a barrier for effectiveness, while intrasectoral resistance across levels delayed adoption. WhatsApp facilitated networking, capacity building, and adoption. Rushed scale-up generated barriers for quality delivery and led to different implementation pathways across municipalities. Legal institutionalization is critical to assure permanent funding and maintenance. PCF has enhanced early childhood services in Brazil, but strong negative feedback loops need to be addressed for effective sustainability.