There's Cristofori music school at Woodlands. They have fun classes from 20 months onwards.
depends on interest of the child.....sports, vocals, musical instruments, dramatics, dance
Hope this article helps : https://sg.theasianparent.com/classes-for-babies-in-singapore/
i see mostly at civic centres has most enrichment classes during weekends.
Arts & Crafts, Dance/Ballet lessons, Music lessons are quite interesting
Try physical activities like swimming?