Complex sentence: His first ink-spattered composition and his precocious efforts with the violin were of his own initiative, and came as a surprise to Leopold, who eventually gave up composing when his son's musical talents became evident.
Split into simpler sentences: His first ink-spattered composition and his precocious efforts with the violin were of his own initiative, and came as a surprise to his father. Leopold eventually gave up composing when his son's musical talents became evident.