Children were central to Dutch and Belgian colonial projects. Children and youth were the objects of colonial interventions issued by missionaries and officials. However, children could also become actors who produced change in a colonial context. Crucial in colonial policies towards children was the separation of children from their parents, communities and/or culture ('child separation') in all kinds of forms - temporary or permanent, far from home or close by, in contact with their own community or cut off from it - and to various degrees of coercion (voluntary, from a situation of dependence, enforced with punishment or violence). Child separation projects could involve adoption, foster parenting, 'apprenticeships' serving a household, boarding schools or day schools. It could concern children from the local elite, but also children who ended up on the margins of their own communities or were even bought out of slavery. Child separation was never about education only, but always imposed specific morals and life styles on its subjects as well. It caused profound fault lines in colonised families and communities. For colonial politics, it was key to controlling, influencing and disciplining the colonised population ('governmentality'). In the case of children of ethnically mixed descent, child separation often involved policing hierarchical racialised boundaries in the colony; in the case of indigenous children, it aimed at transforming the colonised population. Christian missions were pivotal in child separation projects. This special issue, therefore, pleads for a more central place of Catholic and Protestant missions in the analysis of Dutch colonial history, comparable to Belgian historiography. Finally, it is precisely these (missionary) colonial projects, often labeled as 'soft' or 'civilising', that have passed unnoticed into post-colonial discourses, organisations and practices, such as transnational adoption or surrogacy, and countless development projects in which children, detached from their own ...