Every citizen can dispose of his/her property as he/she likes, including by gifting it. Inheritance law imposes a restriction on the size of the asset the person can dispose of without consideration in relation to the person's whole estate. One can only make gifts or dispose freely and incontrovertibly within the limits of one's disposable part. The share is disposable if the testator has direct heirs - children, grandchildren, a surviving spouse or surviving parents. These are the three categories of heirs (children, parents and spouses) to whom the law has guaranteed part of the testator's assets and who are entitled to a reserved share. The disposable share is the difference between the sum of the testator's assets and the reserved share. There are no obstacles to someone gifting assets directly to his/her grandchildren, whether or not the donor's children are still alive. 

Such gift does not exclude the need to respect the disposable share because, if the son or daughter is still alive, they are the original holders of the right to a reserved share, and not the grandchildren. If this right is affected by a transaction without consideration, the heir of the reserved share can challenge the transaction, independently of the person who has received the gift.