This word I am looking for basically describes the quality of a son or daughter who is obedient and devoted to taking care of the elderly parents for he realized the pain and hardship his parents went through in raising him.
You won't find a single word that captures all of that, but "Filial obedience" or "Filial devotion" may be phrases you could use.
Dutiful comes to mind.
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Appreciate it GG!

 Philip's reply was promoted to an answer.
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Maybe I am worng. Dutiful -to me has an element of obligation and the word I have in mind should carry a sense of , like GG's suggestions, appreciation toward the parents' hard work and devotion in raising their children. Anyhow, Thanks.