When do I have to start thinking about preschool for my child in Singapore?

It varies on which school that you intend to put your child in. The popular ones usually have a long waitlist so you'll have to put your name down early. Although I heard some would only allow waitlist 6 months prior to enrolment. Those in infantcare are usually automatically be eligible for playgroups so you may wish to consider to enrol your child earlier to secure a spot.