Hi... you can get information Fr community centers near your house. Many community centers organize classes for children including karate class
If you like trying Brazilian Jiu Jitsu, try the Gentle Art Academy. My kids go there and the teachers are absolutely amazing.
Shitoryu Karate Association have classes for kids. You can check out more about her classes here http://ska.org.sg/
You can try searching at one.pa.gov.sg. The community centres hold karate classes that are very reasonably priced.
http://sg.theasianparent.com/best-martial-arts-classes-for-kids-in-singapore/
thanks