This study explores the musical content and human processes of improvisations of children and adults using the phenomenological lenses of time, space and responsivity. Paired improvisational performances of two late-career adult composers and two 7-year-old children were analysed considering a lifespan-related perspective involving the origins of spontaneous musical creativity associated with childhood dispositions and the musical expertise gained from practice, training and experience. Findings suggest that origins and expertise are operating in improvisational experiences of children and adults. Implications are drawn for musically meaningful research and evaluation of children's improvisations.