Children who have survived a life-threatening disease like cancer benefit from social support from other children with a similar background. However, these children are often geographically dispersed and have little opportunity to meet. We investigate the design and development of Digital Peer Support Services (DPS), which may overcome this problem. Peer support is a kind of social support that brings together peers with similar experiences to help their adjustment to a disease. The aim of this paper is to develop design patterns for social interaction that can be implemented in a DPS for children surviving cancer. We conducted four sets of design workshops with children, from which emerged clusters relating to peer support and friendship that were broken down into triads. From these, six design patterns for social interaction were developed. The patterns delineate different aspects of social interaction for children and are illustrated with examples from DPS prototypes and concepts. The patterns are organized into a hierarchy, comprising the beginning of a design pattern language for social interaction for children. An essential aspect of the patterns is providing users with transparency and control of the extent to which their social interaction is public or private. Copyright © 2014 ACM.