Accounts of the Mozart children at play recall accounts of the infant Brontës: Wolfgang's elder sister Nannerl told of the day when - for lack of anything better to do - the eight-year-old composer began to write his first symphony, and asked her to remind him 'to give the horn something worthwhile to do". As Leonidas Kavakos and the Camerata Salzburg demonstrated in their late-night Prom, she did just that, as the second movement gives the horn a starring role in the dreamy miasma the orchestra sets up.
This 12-minute work is not in itself evidence of overpowering genius - Mozart was less of a prodigy than is sometimes claimed - but it reveals a remarkably assured control of orchestral effects. It shows no startling originality in the development of its ideas, but it could pass as a mature work by one of the adult composers working then in Salzburg. Full marks to Nicholas Kenyon for according it a Proms premiere.
But the pièce de résistance was Mozart's Third Violin Concerto, written when he was 19 and his genius was bursting into full flower. Kavakos's trademark is clean phrasing and an exceptionally pure tone. Leading with his violin, he came across less as a star-plus-backing than as primus inter pares, the inspirational leader of the pack.
His first-movement cadenza was discreetly dazzling. In the unfurling of the Adagio - which Alfred Einstein famously said seemed "to have fallen straight from heaven" - Kavakos brought things to a sublime stasis, which his cadenza reinforced with a graceful rumination on all that had gone before. There was no self-promotion in the musical personality he projected, and modesty was the impression left behind.
Haydn's Symphony No 82 is nicknamed "The Bear" thanks to the organ-grinder's drone - on a variety of instruments - that permeates the final movement. It shows Haydn at his most mercurial and inventive, and under Kavakos's direction this small ensemble, with their warm, sympathetic sound, did it proud.
BBC Proms to 9 September (020-7589 8212; www.bbc.co.uk/proms)