Yes, they do. They owe them respect as they owe all people. They also owe them to continue putting effort into making the best of their lives and not waist their parents’ investments. There is however no obligation to care etc.. from child to parent. When your child has grown up, then as a parent you may still have a function as a grandparent, but when it comes to obligations, I feel it is a one way street. (Don’t tell my twins, yet.) I think that children may have obligations to their parents, but those have to be earned by these parents. They do not stem from merely being biological parents. I teach my children that helping other people is an obligation in general and in particular for the ones you care about. We’re social animals, after all, aren’t we?