The most common and most likely answer to this crossword clue is the 5 letter word KIDDO
K
I
D
D
O
More clues leading to the result KIDDO
Buddy explains!

The straight part
We know that "Son" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case son = kiddo.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.
What does KIDDO mean?
KIDDO noun- A close friend; especially used as a form of address.
- A child.