This study examined physiological effects of separation and reunion in a sample 3- to 6-year-old children. Using continuous ambulatory recording, changes in heart rate (HR), respiratory sinus arrhythmia (RSA), and pre-ejection period (PEP) were compared across the episodes of a separation–reunion procedure based on the strange situation. RSA decreased significantly over the course of the procedure as well as on separation from the parent and not the stranger, supporting that separation from the attachment figure elicited vagal withdrawal in young children. The absence of significant PEP effects suggest that the separation–reunion procedure, and more specifically separation from the parent, was not threatening enough to activate the sympathetic nervous system, even if children were insecure attached and inhibited with regard to strangers. Some of the variability in HR increases to reunion was explained by younger age. The findings highlight the role of the ANS as a regulatory process in the parent–child relationship. © 2007 Wiley Periodicals, Inc. Dev Psychobiol 49: 119–128, 2007.

Among children placed out of home, behavioral and relationship functioning is often problematic. When placed in foster care, problems tend to persist or even worsen and increase the risk of placement breakdown. Multidimensional Treatment Foster Care for Preschoolers is an intensive behavior-focused program for young foster children (3 to 7 years) aiming to provide children with a positive and stimulating foster family setting and individually tailored behavioral interventions. This study will be the first to examine the effectiveness of Multidimensional Treatment Foster Care for Preschoolers outside the US and to examine the effectiveness across a broader range of problems related to foster care.