The gift may likewise be revoked, even if the donee has come into possession of the property given and has been left there by the donor since the birth of the child. However, the donee is not obliged to return the fruits he has received, of whatever nature, if not from the day on which the birth of the child or his adoption in plenary form was notified to him by writ or other act in good form, even if the request to re-enter the donated property was made after that notification.