Once a child reaches 18 years old, he or she is legally an adult. Once they cross that threshold, regardless of your child's medical conditions, he or she has all the rights afforded to an adult—including the right of self-determination. In theory, this means they are able to make their own decisions without your input (and those decisions cannot be taken from them without their consent).

In very rare cases, however, parents are given rights of guardianship over an adult child.

While adult children are no longer legally the responsibility of a parent, he or she may still need your care and supervision. If your child has a condition that demands special care—such as autism or Down's syndrome—then the line between what the law demands of you and what your child needs becomes complicated.

Sometimes, men and women with special needs lack the capability to make wise decisions and need someone to help guide them. To help with that very problem, Scottish lawmakers created an Adults with Incapacity Act.

The AIA gives aid to adults who are not able to make informed decisions or manage their own independence 100% of the time. It accomplishes that in part by granting another adult the power to make decisions on behalf of someone who cannot choose for themselves. It also protects their finances and medical care through the appointment of a financial guardian and another with the power of attorney.

If your son or daughter is still living at home, the court may appoint a social worker to help mediate between your desire to care for your child and your adult child's right to make their own decisions. Social workers can also help you by providing an expert opinion. Specialized social workers are trained to work just with individuals with acute needs.

If your child with neurological differences chooses to leave home, then your right as a parent to serve as their guardian is difficult to navigate. The NHS says that a care manager should be involved in any decision and talk with the adult's parents. A care manager can recommend placement, which may mean moving the child out from his or her parent's care while still ensuring their long-term well-being.

Many parents take on the role as their child's advocate well into adulthood. For more information on your state policies on adult children with autism, speak with a family law attorney. Each case is unique, so hiring experienced legal help to sort through your situation may help provide answers that general information cannot.