For my elder son, i did not send him to any class. only when he attended Playgroup in Mar this year, i enrol him in the Gymkidz class offered by the Childcare centre
But some of my friends actually send their child for Music Appreciation class (Kindermusik) when they turn 6 months. You may check out their website.
Children Music Class - Music Classes for Kids and Babies - Kindermusik Asia