Foster placements are more likely to break down where the foster carers already have birth children. Studies that explore the impact of fostering on foster carers and their birth children have suggested that relational changes occur, but these changes have not been examined in depth. This study aimed to explore the impact of fostering on parent-child relationships within foster families. Nine foster carers (including three couples) were interviewed separately, and the data were analysed using constructivist grounded theory methods. Analysis indicated that birth children may attribute particular importance to their position in the family (e.g. oldest child, youngest child) and that this is a key element of the way in which they relate to their parents. Emotional security and parent-child relationships can therefore be strained by a foster placement not taking this into account. Foster children also introduce significant competition for parental resources, putting a strain on relationships. Foster carers seem to prioritise, consciously or not, the preservation of relationships within the biological family. Reflecting on relationships and making changes to maximise potential improvements in relationships can lead to positive outcomes, and this can have an impact on whether families continue fostering or not.

The relationship between foster children and carers' own offspring has been investigated in many studies within foster care. However, while general patterns and outcomes have been established, the explanations underlying this relationship are more likely to be found in the common themes of smaller studies based on psychological theories published in academic and professional journals. This review by Hayley Thompson and Susan McPherson examines 14 published articles describing 12 different research studies, all exploring the experience of living with foster siblings, as described by the birth children of foster carers. These 12 studies include primarily qualitative evidence, although four also use forced choice and open response questionnaires. Taken together, the studies reviewed reflect the experiences of 1,102 children, aged between three and 32 years. They discuss the positive gains of fostering, the experience of loss, the conflict experienced, the transitions made and ways in which children manage the foster sibling relationship. These findings are discussed in relation to psychological theories, and proposals for future research and clinical practice are outlined. Conclusions are also drawn about the contribution of small-scale studies published in journals in disseminating research findings about fostered children.