While no one likes to think about their own mortality, it is always wise for parents to prepare for their unlikely departure. This is particularly important when it comes to a child with special needs, because you will want to ensure that everything is properly in place to care for your child. In addition to a will which lays out how your estate is to be dispersed, you will need a special needs trust (or sometimes called supplemental needs trust) for your child with Prader-Willi syndrome in order to preserve their eligibility for SSDI or SSI, Medi-Cal (Medicaid outside of CA) and any other benefits.
The laws governing wills and trusts vary state to state and change periodically, therefore it is important that you consult with a professional who is familiar with CA laws and to also periodically review your will and trust to make any necessary updates due to personal changes or changes in the law.
A mother of a child with PWSA of Colorado is an attorney by profession and offers this brochure as an overview of wills and trusts.
The California Bar Association maintains a referral service. The Special Needs Alliance website has a free trustee handbook that you can either download or have mailed to you. They also have a list of attorneys to help you locate someone to prepare your will and special needs trust.
PWSA has a product, Estate and Guardianship Presentation (item #255), which is available for purchase through their website.
PWCF maintains online and in-person Support Groups for parents and professionals.
PWSA (USA) maintains several Facebook support groups.