What documents do I need if my child has a different surname from one parent when traveling through Vietnam?

If the mother's surname differs from the child's (while the father and child share a surname), border officers may ask questions. Bring the child's birth certificate to prove the family relationship, and consider a notarized parental consent letter from the other parent.

You do not need to replace a child's passport just because the photo no longer matches their current appearance — the passport remains valid until its expiry date. One traveler confirmed successfully using their daughter's passport issued at 4 months old when she was already 10 years old.