Here are some resources to gain a better understanding of:

Autism

Autistic Self Advocacy Network | Nothing About Us Without Us

Autistic Women & Nonbinary Network (AWN)

National Autistic Society (UK)

Autistic Inclusive Meets

Down Syndrome

Global Down Syndrome Foundation

Human Rights Organization for Individuals with Down Syndrome

National Association for Down Syndrome

ADHD

Children and Adults with Attention-Deficit/Hyperactivity Disorder (CHADD)

Attention Deficit Disorder Association

ADHD Center for Success

ADDitude - Inside the ADHD Brain: ADD Symptom Tests, Treatment, Support

Cerebal Palsy

Cerebral Palsy Group

United Cerebral Palsy

General

Neurodiverse Self Advocacy

Special Olympics

Learning Disabilities Association of America

Different Brains

Communication First