Background: Attachment quality may affect psychological functioning. However, evidence on attachment representations and their correlates in children born to parents with schizophrenia and bipolar disorder is sparse. Methods: We compared attachment representations in a Danish sample of 482 children aged 7 years at familial high risk of schizophrenia, bipolar disorder, and population-based controls and examined associations between attachment and mental disorders and daily functioning. Attachment representations were examined with the Story Stem Assessment Profile (SSAP). Mental disorders were ascertained in diagnostic interviews. Daily functioning was assessed with the Children's Global Assessment Scale. Results: We found no between-group differences in attachment. Higher levels of secure attachment were associated with decreased risk of concurrent mental disorders in the schizophrenia high-risk group. Higher levels of insecure and disorganized attachment were associated with increased risk of mental disorders across the cohort. Higher levels of secure and insecure attachment were associated with better and poorer daily functioning, respectively. In the current study, results regarding defensive avoidance could not be reported due to methodological limitations. Conclusion: Familial high risk of schizophrenia (FHR-SZ) or bipolar disorder is not associated with less secure or more insecure attachment at age 7. Insecure and disorganized attachment representations index risk of mental disorders and poorer functioning. Secure attachment may be a protective factor against mental disorders in children at FHR-SZ. Validation of the SSAP is needed.