The most common and most likely answer to this crossword clue is the 3 letter word ACT
I've seen this crossword clue in Financial Times
A
C
T
More clues leading to the result ACT
- Do something in law
- Agreement, heading off item of legislation
- Leads for amazingly competent thespians in play
- Tread the boards at Criterion theatre, taking leading parts
- Take steps in a court
- Agreement with no power in law
- Function of a court
- Diplomatic behaviour, heading off legislation
- Pressure to abandon agreement? It may be just a pose
- Take steps to perform on stage
Buddy explains!

The straight part
We know that "Kid" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case kid = act.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 ACT mean?
ACT noun- Something done, a deed.
- Actuality.
- Something done once and for all, as distinguished from a work.
- A product of a legislative body, a statute.
- The process of doing something.
- A formal or official record of something done.
- A division of a theatrical performance.
- A performer or performers in a show.
- Any organized activity.
- A display of behaviour.
- A thesis maintained in public, in some English universities, by a candidate for a degree, or to show the proficiency of a student.
- A display of behaviour meant to deceive.
- To do something.
- To do (something); to perform.
- To perform a theatrical role.
- Of a play: to be acted out (well or badly).
- To behave in a certain manner for an indefinite length of time.
- To convey an appearance of being.
- To do something that causes a change binding on the doer.
- (construed with on or upon) To have an effect (on).
- To play (a role).
- To feign.
- (construed with on or upon, of a group) To map via a homomorphism to a group of automorphisms (of).
- To move to action; to actuate; to animate.