Language disorders are associated with difficulties in various aspects of life, such as academic and social functioning, resulting in impaired health-related quality of life (HRQoL). Most studies use a parent proxy method to assess HRQoL. Since HRQoL refers to the subjective experience of an individual, it is necessary to assess children’s perspectives along with their mothers’. The aim of the current study is to explore HRQoL rating agreement between children and their mothers, since the literature on other conditions suggests that discrepancies seem to reflect their different perspectives. Thus, 53 Greek-speaking children diagnosed with DLD attending kindergarten and their mothers completed, respectively, self-report and parent proxy PedsQLTM questionnaires. Mothers reported significantly better HRQoL than their children with developmental language disorder (DLD) in all HRQoL domains (p < 0.001). Poor agreement was revealed after comparing the scores from both responders, both in abstract domains, such as emotional functioning, as well as in more observable ones, such as physical health (ICC ranged from −0.05 to 0.07). Bland–Altman plots also showed poor agreement on HRQoL. Our results expand on the already known, from other conditions, importance of evaluating children’s subjective experience of their HRQoL in kindergarten children with DLD. A multi-informant approach is ideal, and clinicians should prioritize children’s view about their lives even when they are kindergarten-age. This approach could inform interventions focusing not only on language skills but also on other areas where it is necessary, depending on the child’s subjective experience combined with the maternal perspective.