Previous research has shown that children can be trained to interpret ambiguous interactions with mother in a more secure way by use of a CBM procedure. A secure attachment-related processing bias can causally increase children's trust in mother's availability. The present study tests whether intranasal administration of oxytocin can increase the effect of a secure cognitive bias training. Oxytocin is a neuropeptide that is involved in human attachment and bonding. Intranasal administration of oxytocin can increase trust among people. After oxytocin or placebo administration, children are either trained to interpret ambiguous interactions with mother in a secure way or receive a neutral training unrelated to interpretation of maternal behavior. Pre- and post-intervention children's trust in mother, support seeking behavior and interpretation of maternal behavior is assessed. Moreover, possible oxytocin side-effects will be monitored.