Religion is a system of beliefs and practices that unites people into a community. Religiousness can be manifested through ideological, ritualistic, experiential, intellectual and consequential dimensions. Parental religiousness can guide children’s morality and behaviours. In fact, several scholars are concerned if religion makes children into better citizens. To better understand the growing research on how religion relates to child development, and in particular, prosociality, a systematic review was conducted in Spring/Summer 2021. The focus of this review is children between the ages of three and ten years since these are the years of heightened religious and prosocial development. Eligible studies included published research on the association between religiousness and children’s prosocial behaviour. From 1976 to May 2021, 203 studies were identified. Blinded double screening of abstracts and full text using the eligibility criteria, 100% agreement, identified a final sample of nine empirical papers. Data extraction included summaries of measures of religiousness and prosocial behaviour, methodological characteristics, and the associations. Narrative synthesis was used to address the three research questions. Six of the nine studies found a positive association between religiousness and children’s prosocial behaviour. This systematic review found that religiousness is mostly measured through religious affiliations, and only three studies measured prosocial behaviour in general. The other studies focused on empathy and/or altruism as a prosocial construct. The studies in this review present a lot of variations across demographic variables, methodological characteristics, and overall quality. In addition to this empirical synthesis, the systematic review reveals that research in this area is scarce. This review concludes with implications for future research, such as a focus on the early years and the targets of children’s prosocial behaviours.