Bava Batra 132 - Giving All Property to Administrator

If one writes in his will that he is giving all his possessions to his wife, he has only made her an administrator over his estate; she does not actually acquire it.

The Sages determined that a man would not strip his sons of their entire inheritance; therefore, it is assumed that he is merely appointing her as an administrator, because he wants them to treat her more respectfully. The administration lasts only while the children are minors. The ruling applies only if he left over all his property to his wife, but if he left anything to his sons, the gift to his wife was genuine.

Art: Ary Scheffer - Marie Joseph Marquise de La Fayette, on his Deathbed