The psychosocial consequences of growing up with Heritable Connective Tissue Disorders (HCTD) are largely unknown. We aimed to assess Health-Related Quality of Life (HRQoL) and mental health of children and adolescents with HCTD. This observational multicenter study included 126 children, aged 4–18 years, with Marfan syndrome (MFS, n = 74), Loeys–Dietz syndrome (n = 8), molecular confirmed Ehlers–Danlos syndromes (n = 15), and hypermobile Ehlers–Danlos syndrome (hEDS, n = 29). HRQoL and mental health were assessed through the parent and child-reported Child Health Questionnaires (CHQ-PF50 and CHQ-CF45, respectively) and the parent-reported Strengths and Difficulties Questionnaire. Compared with a representative general population sample, parent-reported HRQoL of the HCTD-group showed significantly decreased Physical sum scores (p < 0.001, d = 0.9) and Psychosocial sum scores (p = 0.024, d = 0.2), indicating decreased HRQoL. Similar findings were obtained for child-reported HRQoL. The parent-reported mental health of the HCTD-group showed significantly increased Total difficulties sum scores (p = 0.01, d = 0.3), indicating decreased mental health. While the male and female MFS- and hEDS-subgroups both reported decreased HRQoL, only the hEDS-subgroup reported decreased mental health. In conclusion, children and adolescents with HCTD report decreased HRQoL and mental health, with most adverse outcomes reported in children with hEDS and least in those with MFS. These findings call for systematic monitoring and tailored interventions.