I am thankful of my parents. Because they always support me under whatever situation and give me best living conditions. They bring up me and send me to study. So I am very thankful of my parents.
I am thankful for my parents because they always support me under whatever situation and give me the best living conditions. They bring me up (better: they have raised me) and send me to study. So I am very thankful for my parents.
be thankful FOR something/someone. Give thanks TO someone