You can submit the extension of stay form at least 7 days before the expiry of your child’s current Special Pass.

You are required to furnish the following documents for the extension of your child's special pass:

a) Travel documents of both parents,

b) Singapore IC or work passes of both parents;

c) Parents' marriage certificate (if any) and child's birth certificate;

d) Advisory note; and

e) Letter of acknowledgement from the Embassy or High Commission in Singapore indicating you have submitted a travel document application for your child or the travel document for your new-born child.

This information is sourced from ICA