You may want to review universal life policies for each spouse. You will have to review your financial situation with to determine what would be best for you. Check with your Medical Insurance Carrier to see if the child would be covered after age 18. Some policies and states require that coverage be extended to family members with disabilities. It helps if both spouses are working and able to achieve coverage.
Companies change coverage from time to time.
Make sure during this change that they will still cover your child long term. You may need to establish a special trust to insure that your disabled child will receive the benefits of an inheritance. Generally any assets the child has upon reaching age 18 will be tapped first for any governmental programs. This need to be carefully drafted by a specialist in this area. If necessary, you will need to have a guardian named for your child if they are not competent upon reaching age 18.