Early childhood care and development has increasingly become a part of the global development agenda. Fueled by a threefold rationale, rooted in development psychology, social economy, and human rights, the arguments for investing in early childhood care and development are virtually unassailable. However, this rationale is somehow at odds with insights developed within the sociology of childhood, emphasizing childhood as a social construction amendable to context and children's own agency. Inspired by the methodological approach known as institutional ethnography, we explore how development aid workers respond to and enact the early childhood care and development mission. Building on interviews with development aid workers in Phnom Penh, Cambodia, we describe how their actions, when justified, enter into institutional circuits where the demand for evidence is striking. By exploring development aid workers' own work knowledge, including how they strive to be compliant with the early childhood care and development rationale, yet also oppose it, our contribution points to the importance of re-negotiating evidence in order to discover the blind spots that may be concealed within what we refer to as a "justification loop."