I think beyond even having supportive parents, the most important part was that he had a parent that had a degree in the field that he happened to be a genius in. His mother knew exactly how to guide her child through the material, even if it just was to let him go off to a corner and read the books she guided him towards for 3-4 hours a day for fun. So many children have advanced proclivities for certain things and parents that just can't even see what it is their child is brilliant at.
Having someone that knows the path and can point it out to them is a beautiful thing to have as a child.