A reader complements this post:
I may have been the brat in The Giving Tree once upon a time. But now that my father suffers from late-stage Alzheimer's, our roles are reversed. I visit him in his care home, feed him, get him up to walk while holding his hand tightly in case he takes a bad step. I tell him loudly, "I love you, Dad," even though he never says it back anymore. I hang on every word he says because he says so few. Every time he says, "My daughter!" my heart sings because so often I get nothing but a blank stare from him.
The thing is, I'm so grateful to do for him whatever he needs because he did so very, very much for me. Near the end of his life, I'm the one giving back and I'm glad to do it.