For a 3-year old, you can consider English Soccer School or Tinytots. I’ve read good reviews for both stating that the lessons were fun and coaches were engaging and attentive to the children. You can sign up for free trials (offered at both places) while you consider. You can refer to their websites for more information (schedule, locations and fees etc) English Soccer School http://englishsoccerschool.com/our-programs/recreational-fun-football/ Tinytots http://www.tinytots.com.sg/tinytotssoccer/ Hope your child will have a fun time!
You can trySport4Kids. It teaches basic soccer skills like passing, control, speed, and movement for kids as young as 18 months in a secure and non-competitive environment. Classes are held at various locations around Singapore, you can check their schedules here: http://www.sport4kids.sg/class-schedules-2/ Tel: (+65) 9355 0376