Although bats are highly social mammals, the mechanisms influencing the establishment of social structures are far from being fully understood. So far, no study has addressed the effects of spatial proximity between newborns such as that occurring in nursery clusters on the development of preferential associations among individuals. We tested such effects on captive pups of Kuhl’s pipistrelle Pipistrellus kuhlii. During the first 6 wks, we kept them in separate rearing groups. Once able to fly, bats were allowed to freely interact in a common flight room, where those reared in the same groups showed higher rates of amicable interactions (proximity during roosting, allogrooming, huddling) but no effect on aggressive behaviour. Sex also influenced such frequencies, females being more likely to interact amicably. The phenomenon we describe may have significant implications for the development of bat social structures, including colony aggregation, within-colony cryptic subunits or preferred association of individuals in fission–fusion dynamics. Our study adds a further dimension to bat sociality, highlighting the implications of spatial proximity in an early age phase.