Short answer. Yes. The Civil Code allows ratification to be effected by the guardian of the incapacitated person, so a guardian can confirm a contract the minor signed alone and close off the right to have it annulled later on the ground of minority.
What the law says
Ratification may be effected by the guardian of the incapacitated person.
Civil Code, Article 1394 — Ratification by the Guardian. Read the full provision →
The contract is voidable, not void
A contract signed by a minor acting alone is not a nullity. It is voidable: it produces effects and binds the other party unless and until it is annulled at the instance of the person the law was protecting. That distinction is what makes ratification possible at all. A void contract - one with no object, or one the law forbids outright - cannot be saved by anyone's confirmation, no matter how willing. A voidable one can, because the only defect is the missing capacity of a party whose interest the law guards, and the guard may decide the bargain is worth keeping.
What ratification by the guardian actually does
Ratification cleanses the contract of the defect from the beginning. Once the guardian ratifies, the minority can no longer be raised to annul it, and the agreement stands as though it had been properly entered into from the start. The other party cannot object; he never had the right to annul in the first place, since the remedy belongs only to the incapacitated side. Ratification need not be a formal document. It can be express, or it can be tacit - shown by the guardian executing the contract, accepting its benefits, or otherwise acting in a way that plainly treats the agreement as binding, with knowledge of the reason it could have been annulled.
Who counts as the guardian, and the limits on the power
The person ratifying must actually hold authority over the minor's person or property - a parent exercising parental authority, or a guardian appointed by the court. A relative who happens to be caring for the child does not qualify simply by being the nearest adult. The power is also fiduciary rather than personal: a guardian acts for the ward's benefit, not his own, and ratifying a contract that strips the ward of property at a poor price is an abuse that can be attacked on its own footing. Where the transaction disposes of the ward's real property or substantial assets, court authority is ordinarily required, and ratification cannot be used as a shortcut around that requirement.
The minor can also ratify - but only later
The guardian is not the only route. The minor may confirm the contract himself once the incapacity has ceased, that is, upon reaching majority and with knowledge of the ground for annulment. Until then, ratification by the minor alone is ineffective, because the very defect being cured is his lack of capacity. The practical consequence for the other party is that the deal sits in limbo: it can be annulled within the period the Civil Code fixes for actions to annul, counted from the time the incapacity ends. Anyone contracting with a minor should therefore secure the guardian's participation at the outset rather than rely on later confirmation.
Practical points
If you are a guardian weighing whether to ratify, get the contract valued before you confirm it, and put your decision in writing so the date and scope are clear. If you are the counterparty, keep proof of the guardian's authority and of the ratification itself. This is general legal information rather than advice on your situation, and no result is promised - transactions involving a ward's property are worth reviewing with counsel first.