I don't think raising my children to take care of me when I'm old (should be any day now) would be acting in my self-interest. In fact, I think it would be acting against my self-interest.
A better model, I think, is for me to do all that I can to be self-sufficient, and not predatory in nature, in terms of expecting other people to care for me.
As long as I can find pleasure in life and activities that interest me, like hacking in Lisp, or re-learning how to weld, or reading about philosophy, I'd like to go on living.
When there are no longer reasonable things for me to pursue, then it's time to go. I certainly don't expect my children to do anything more for me than they freely wish to do.
Children are not born to be servants to their parents, as you observe. That's why I think it's incumbent on parents to treat their children as best as they possibly can, since children come into a family without being able to consent, and since children are essentially powerless to leave a family that treats them poorly, until they reach some age where they can be self-sufficient.