Based on a transactional model of children's development under family stress this study investigates:a) family stress caused by dysfunctional family processes such as interparental conflict, inadequate parenting, and low quality of the parent-child-relationship,b) the mediating function of emotion processing (emotion regulation, (in)secure attachment) for the relation between family stress and children's mental and physical health, behavior problems, and well-being, andc) the stress buffering function of the quality of the children's peer relationships.The children undergo a specific vulnerable phase for stress: the onset of puberty. This transition might influence the family relationships as well as the adjustment to family stress.