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.
The basic idea is that in a "silent trust," the terms of the trust prohibit the trustee from telling the beneficiaries about the trust or the assets in the trust. You should know that these trusts are legally controversial and are not allowed in all states.
Some states mandate that the trust beneficiaries must be told about the trust upon reaching a certain age. Delaware, however, is one state that does allow silent trusts in almost all circumstances.
If you are interested in such a trust, then contact an experienced estate planning attorney to explore your options.
Reference: Financial Planning (October 16, 2015) "How Silent Trusts Can Help Your Clients"