Extraordinary musicianship in children and notions of genius are closely entwined, but these concepts need to be historicised if we are to understand how such connections came about. This chapter explores child performance in the increasingly competitive and commercial concert-life of eighteenth-century London, examining how juvenile musicians were presented and themes that characterised their reception. Mozart appeared before London audiences in 1764–65, as a cosmopolitan virtuoso from Salzburg, coached and promoted by his musician father as ‘a Prodigy of Nature’, a phrase then unfamiliar in English musical discourse. The chapter shows that while the Mozarts’ campaign in London did much to establish a new archetype of the ‘musical prodigy’, this developed in dialogue with local cultural, musical, and intellectual contexts, audience expectations, and the vagaries of the professional environment.