Where did Wolfgang Amadeus Mozart start being a musican?

Mozart came from a very musically-inclined family. His father Leopold was Vice-Kappellmeister (concert master) to the court in Salzburg, and it was natural that he would raise his two surviving children to play and compose music as well. Both children were talented musicians, but Wolfgang's older sister, Nannerl, was discouraged from utilising her creative talents.

Leopold trained his son intensively in playing both the violin and klavier/piano right from the time his son was a toddler, and he actively pursued opportunities to show off his son's talents. Young Wolfgang Amadeus was paraded as a "wunderkind", a wonder-child or prodigy, and being so young (and somewhat small in stature, due in part to frequent illnesses) he was received with great favour at the courts of the nobility and aristocrats.

Until the 19th century music was considered to be a trade rather than an artistic calling and was simply handed on from father to son, so most composers born before about 1800 had parents or other close relatives who were musicians (eg Bach, Mozart and Beethoven). One of Mozart's two surviving sons also became a composer, although he wasn't famous.