Motivation is a crucial aspect of learning, particularly in the field of music. For decades, motivation for learning music has been a much-discussed subject, and yet its influence still remains a convoluted issue. This study systematically analyses peer-reviewed English language studies, according to PRISMA guidelines, in order to understand how children's and adolescents' motivation to learn a musical instrument has been studied, the theories that have been adopted to frame this research, the types of quantitative instruments that have been designed or adopted within the research designs, and the types of findings that have documented. A search on "Web of Science," Education Resources Information Center, and "Scopus" was conducted, using the following terms: music, instrument, learn, education, study, and motivation. The initial search identified 447 studies. Twenty of these met the inclusion criteria for investigating any music-related aspect of motivation that was based on the analysis of quantitative data. Results show a limited number of studies that have explored children's motivation in the context of learning a musical instrument and report a special focus on the central role of parents and social background. Implications of these results for music education and the adequacy of questionnaires to children are discussed.