If your child is male, he must register with the U.S. Selective Service, even if he has a disability and regardless of the nature of the disability. This includes people who identify as transgender but who were assigned male at birth. Females, including transgender people assigned female at birth, are not required to register at this time.
FAST FACT:
While disability may disqualify your child from the service or from the draft (if a draft is ever reinstated), it is still the law that they register. Your child or you (on their behalf) can register online or print off the registration form and submit it to the Selective Service System.