Every donation inter vivos, made by a person having no children or descendants, legitimate or legitimated by subsequent marriage, or illegitimate, may be revoked or reduced as provided in the next article, by the happening of any of these events:
(1) If the donor, after the donation, should have legitimate or legitimated or illegitimate children, even though they be posthumous;
(2) If the child of the donor, whom the latter believed to be dead when he made the donation, should turn out to be living;
(3) If the donor subsequently adopt a minor child. (644a)