Via Kiplinger:

Anyone with a child with special needs understands the need to prepare for the future. A trust is always a good place to start, and figuring out a savings goal for that trust is a key part to your planning.  One of the most difficult challenges in planning for a child with special needs is figuring out how much money it is going to cost to provide for the child, both while the parents are alive, and after the parents pass someday.  Before diving into the latter financial side, what is special needs estate planning? The crux of it is a special needs trust, which if properly established and managed, allows an individual with a disability to still receive certain public benefits. Typically, ownership of assets in excess of $2,000 would cause the individual to become disqualified from certain public benefits. Assets held in a special needs trust do not count toward this amount.  Even if the child is not receiving benefits, families may still want the money protected from the child’s financial choices or those who may try to take advantage of them.

Source/more:  Kiplinger