Music affects a child's intelligence. At what age to start and which instrument to choose?

The exciting discovery that listening to Mozart's music contributes to the improvement of a child's intelligence already during prenatal development was not confirmed, and the Mozart effect was ranked among the biggest scientific mistakes of modern times. However, the question of whether a child's intelligence is related to music does not let scientists sleep even today, and they recently found that children who are engaged with music have better grades in school. When to start with music and which instrument to try first?