The most common and most likely answer to this crossword clue is the 14 letter word FROMÂ THEÂ HEART
I've seen this crossword clue in The Guardian
F
R
O
M
Â
T
H
E
Â
H
E
A
R
T
Buddy explains!
The straight part
We know that "When moved, mother and father may talk thus" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when moved, mother and father may talk thus = from the heart.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.