Researches about foster care rarely involve birth children of foster family. How can concepts of foster parenting and fraternal experiences contribute to understand the relationship and the bond forged between foster and birth children? The study sample included 45 birth adolescents ranging in age from 11 to 18. Semi-structured interviews were analysed using a textual data analysis software (Alceste). Our results show the existence of a singular dynamic professional socialization by birth adolescents, a certain risk of feeling overwhelmed with relationship problems and contrasting family membership. The analysis of these singular fraternal experiences allows to assess the importance of their commitment to a greater recognition and an efficient support. (C) 2016 Societe Franyaise de Psychologie. Published by Elsevier Masson SAS. All rights reserved.