Creating a tool to keep a trust secret from an heir may be considered a "first world" problem, but it is a problem nonetheless. Wealthy families who value their accomplishments are concerned that heirs who know that they are going to receive large amounts of wealth through a trust may not be motivated to establish their own careers or take their studies seriously.
One way to help avoid this is to create a trust that does not give anything to the beneficiaries until they reach an age where they will have settled into their adult lives. However, there still might be a fear that if a beneficiary knows that a large inheritance is eventually coming through the trust, they will not be as motivated to earn their own money as they otherwise would be.
A recent article by Financial Planning, "How Silent Trusts Can Help Your Clients," discusses a type of trust that can be used to keep beneficiaries in the dark about their trusts.