Short answer. The minor's natural guardian or next-of-kin. Labor Code Article 105 provides that if any of the heirs is a minor, the affidavit shall be executed on his behalf by his natural guardian or next-of-kin, rather than by the minor personally, so the employer can pay the deceased worker's wages to the heirs.
What the law says
If any of the heirs is a minor, the affidavit shall be executed on his behalf by his natural guardian or next-of-kin.
Labor Code, Article 105 — Direct Payment Of Wages. Read the full provision →
Why an affidavit is used at all
Article 105 lets an employer pay a deceased worker's wages directly to the heirs without the necessity of intestate proceedings. That is a real shortcut, since it avoids the heirs having to go through a full estate settlement just to collect wages already earned. In exchange for that shortcut, the article requires an affidavit as the mechanism that establishes who the heirs are: the claimants, if they are all of age, shall execute an affidavit attesting to their relationship to the deceased and the fact that they are his heirs, to the exclusion of all other persons.
Who signs when an heir is a minor
That default assumes every claimant is of age. Where that is not true, the article makes a specific substitution: if any of the heirs is a minor, the affidavit shall be executed on his behalf by his natural guardian or next-of-kin. So the minor does not sign the affidavit personally, and the claim on the child's behalf is not simply skipped either. Instead, the minor's natural guardian, ordinarily a parent, or a next-of-kin steps in to execute the affidavit for the minor's share of the claim.
What happens once the affidavit is presented
The completed affidavit is presented to the employer who shall make payment through the Secretary of Labor and Employment or his representative, and that representative shall act as referee in dividing the amount paid among the heirs. Once payment is made this way, the article states that it absolve[s] the employer of any further liability with respect to the amount paid. So the guardian's or next-of-kin's affidavit is not a mere formality; it is what lets the employer pay out the deceased worker's wages, including the minor's share, and be done with that obligation.
This route exists alongside the ordinary rule on payment
This entire mechanism is itself an exception to the article's baseline rule that wages shall be paid directly to the workers to whom they are due. Once a worker has died, direct payment to the worker is obviously no longer possible, so the article substitutes payment to the heirs through the affidavit procedure instead of requiring the estate to go through intestate proceedings first. The guardian's or next-of-kin's signature for a minor heir is simply how that substitute procedure accounts for an heir who cannot execute the affidavit personally.