Perhaps you may click on this two links to help you in your enquiry. One way or another hopefully it answer. https://en.m.wikipedia.org/wiki/Singaporean_nationality_law#:~:text=Entitlement%20by%20birth%20or%20descent,-Individuals%20born%20in&text=Children%20born%20overseas%20are%20Singaporean,years%20preceding%20the%20child's%20birth. https://www.mfa.gov.sg/Overseas-Mission/Ho-Chi-Minh-City/Consular-Services/Registration-of-Citizenship-by-Descent#:~:text=The%20child%20shall%20not%20acquire,or%20after%2015%20May%202004.
Kid can hold dual citizenship until they turn 18yrs old