He has cerebral palsy (mild enough that he can walk, though wobbly). I wonder if his different feet sizes might contribute to his balance problems, as well.
More detail in case it might be related: He has ADHD and Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS is on the autism spectrum). We adopted him, so we don't know a lot of genetic history. Maternal side has history of polycystic kidney disease, high blood pressure and heart disease. He had genetics testing from a major university to rule out Fragile-X and other genetic symdromes.