I think it's because by calling the parents Mr. and Mrs., it shows more respect towards the family
Jana and John-David Duggar are 25-years-old and Jedidiah and Jeremiah Duggar are 16-years-old.
Mrs Duggar teaches her children to be; Attentive Obedience
Joseph Duggar (seventh Duggar sibling) is 22 years old (born January 12, 1995).
The Jim-Bob Duggar family of Arkansas. Mrs. Duggar is expecting child number 19!
In 2012, Michelle Duggar was 46-years-old.
Grandpa Duggar was 73 years old when he died.
Meredith Duggar is 1 year old (born July 16, 2015). She is the 4th child of Josh Duggar.
Marcus Duggar is 4 years old (born June 2, 2013).He is the 3rd child of Josh Duggar.
James Duggar was 3-years-old in 2004.
Josiah Duggar is 18-years-old.
James Andrew Duggar is currently 13-years-old.