Parents give the child a chance to take birth in the physical form. They take care of the child and help him survive in this world. He or she should be grateful to them.
Now the question is how to repay them?

In my opinion, the child could repay the parents by first becoming spiritually independent himself or herself and then helping the parents become spiritually independent too if they already are not.

Parents help their children become at least physically independent and capable. Children should repay them by making them spiritually independent and not emotionally dependent as most parents tend to become!

In my opinion taking physical care of the parents is secondary and taking care of their spiritual growth is primary.

But there are two prerequisites for this to happen, the first being the child himself or herself becoming spiritually independent and second the parents should be receptive enough!

In India there is a famous anecdote of Shravan Kumar carrying his blind father and mother on his shoulders to various temples etc. I am very sure that the anecdote points out towards the spiritual blindness of the parents and their enlightened son lifting them out of their spiritual blindness.