The People in My Life questionnaire (PIML) is one of the few available self-report measures for assessing children's representations of the relationship with attachment figures (parents and peers) in middle childhood. The current study presents validation studies of the PIML in a sample of Portuguese children aged between 8 and 12 years (N = 314) and adolescents aged between 13 and 18 years (N = 281). The original factor structure, composed of a second-order factor of attachment and three first-order factors (Trust, Communication, and Alienation), was confirmed for both scales (Parents Attachment and Peers Attachment) in the sample of children and replicated in the sample of adolescents using confirmatory factor analyses. The Portuguese version of the PIML showed adequate internal consistency and correlated as expected with measures of intrapersonal and interpersonal functioning (internalizing and externalizing problems, prosocial behavior, quality of life, self-compassion, and emotion regulation strategies). The PIML proved to be a psychometrically robust measure of children's representations of their relationships with parents and peers, representing an important advance in the measurement of attachment in middle childhood.