When doing estate planning with an heir who has special needs, you really need to take the time to carefully consider what can be most helpful to them when you are gone. Careful advance planning is the key. If you do it correctly, your assets can change their life, but you have to remember that this all falls on your shoulders. You need to make the proper decisions at the proper time.
Often, this means doing things well in advance. You do not want to take any risks with putting estate planning off until a later date. If you planned to create a special needs trust and never got around to actually doing it, and then you pass away in an unfortunate accident, the ramifications for your heir can be dramatic. For instance, will the money they inherit directly -- without a trust to manage it -- make it so that they cannot get government assistance? It's something you want to think about.