If your parents are unable to care for themselves, it is often an unavoidable feeling. While you tie their shoelaces, change their diaper and help them walk, it does feel like you are now their parent.
Regardless of the circumstances, you are not, and never will be, their parent. Although many of the same techniques work when dealing with them (such as distraction while performing a task), viewing the relationship between parent and child as reversed is potentially dangerous to both of you.