My parents came to my ceremony, but I go to school in my hometown. I expected the ceremony to be a small affair but it was huge! There were tons of parents, siblings, grandparents, you name it. Even the local media was there. It's sort of a nice PR and feel-good event for the school. If your parents want to attend (and you want them to attend) then I'd go for it. There will probably be lots of other families there too.