There are several art classes in Jurong East and Buona Vista (Rochester Mall)! Perhaps you can check them out? Most should have trial classes at discounted rates that you can try out before enrolling :)
No worries :) I think they all have different approaches so do check them out with your son! See whether he enjoys doing art in a guided or freestyle way - then let him decide over a structured program vs a more flexible one :
Jena Lim Xiang Ying