The most common and most likely answer to this crossword clue is the 10 letter word DICKY-BIRD
I've seen this crossword clue in Financial Times
D
I
C
K
Y
-
B
I
R
D
More clues leading to the result DICKY-BIRD
Buddy explains!
The straight part
We know that "What young Robin calls young Martin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what young robin calls young martin = dicky-bird.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.