There is a beautiful and convincing explanation given by the Chinese.....
Thumb represents your Parents.
Second (Index) finger represents your Siblings.
Middle finger represents your-Self.
Fourth (Ring) finger represents your Life Partner.
& the Last (Little) finger represents your children.
Firstly, open your palms (face to face), bend the middle fingers and hold them together - back to back
Secondly, open and hold the remaining three fingers and the thumb - tip to tip
(As shown in the figure below):