Leopold Mozart, a violinist and composer employed by the Salzburg court, married Anna Maria Pertl on 21 November 1747. Shortly after, the couple rented rooms on the third floor of the building at what is now Getreidegasse 9, owned by the Hagenauer family, who were also Leopold's landlords and friends. The apartment was modest — a kitchen, a small storage room, a living room, a bedroom and a study — hardly grand, but centrally placed on Salzburg's main commercial street. Leopold and Anna Maria would raise their family in these rooms for the next 26 years, a period that happened to cover the entire childhood of their most famous son.
Anna Maria bore seven children in the Getreidegasse apartment between 1747 and 1756. Only two survived infancy: Maria Anna, always known as Nannerl, born in 1751, and Wolfgang Amadeus, the youngest, born on 27 January 1756. Child mortality this severe was common across 18th-century Europe, not a mark of particular misfortune for this one family — but it's still the context in which the household actually lived, day to day, for those nine years: every pregnancy a real risk, every surviving child valued and watched accordingly. A family tree displayed in the apartment's hallway sets out the pattern plainly. It's part of why Leopold, once he recognised his two remaining children's musical gifts, invested so heavily and so early in developing them, rather than treating music as an ordinary accomplishment.
Nannerl was, for a period in the 1760s, as celebrated a performer as her younger brother — the pair toured together as child prodigies, presented at courts across Europe by Leopold. As she reached marriageable age, convention closed off the touring and composing career that stayed open to Wolfgang; she continued teaching piano in Salzburg and later married a magistrate, largely stepping back from public performing life. She and Wolfgang stayed close correspondents into adulthood — several of the letters displayed in the museum's later rooms, including one describing his gruelling Vienna schedule, were written to her. Her own musical talent is well documented but never got the same room to develop.