If one of my close childhood friends passed away (and I'm still close to many of them...or at least friendly with them). I would definitely reach out to the parents. I know that when you are a kid friends with a child, that child's family gets to know you every well. You spend the night at their house, come to birthdays, stay over for dinner....all that stuff. I think your presence would be welcomed. Especially since your friend didn't have a family of her own, it would be nice that her parents know that there are others that care about her as much as they do.