A “child psychologist” is a psychologist for children. A “child psychologist” isn’t a psychologist who’s a child, but there are jokes.
 
New York-based stand-up comedian Rodney Dangerfield (1921-2004) said on his television special, The Rodney Dangerfield Show: It’s Not Easy Bein’ Me (1982):
 
“For four years, they (parents—ed.) sent me to a child psychologist. The kid didn’t help me at all!”
 
           
Wikipedia: Rodney Dangerfield
Jack Roy (born Jacob Rodney Cohen, November 22, 1921 – October 5, 2004), popularly known by the stage name Rodney Dangerfield, was an American stand-up comedian, actor, producer, screenwriter, musician and author. He was known for his self-deprecating one-liner humor, his catchphrase “I get no respect!” and his monologues on that theme.
 
IMDb
The Rodney Dangerfield Show: It’s Not Easy Bein’ Me (1982)
1h | Comedy | TV Special 12 May 1982
Rodney Dangerfield’s first ABC special, featuring stand-up and sketches.
 
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One Hundred Albums….
Justin Patrick
7/23/02
“Gall456”  wrote in message
>NO!!! Years ago I went to a child psychologist…that kid didn’t know a
damn thing!
>
 
Oh shit! I haven’t heard someone use that line in years!!
 
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Incredible Rhyme Animal
11/17/04
(...)
I went to a child psychologist. That kid didn’t know nothing!
   
Twitter
James Sadao
@GS_ForTheWin
@cjduc My parents took me once to a child psychologist but that kid didn’t know shit about psychology.
4:25 PM · Jul 23, 2011·Twitter Web Client
 
Twitter
Edward H
@SyntheticPrince
One time I went to a child psychologist. That kid didn’t help me at all.
2:40 PM · Jul 25, 2011·Twitter for iPhone
 
Twitter
Alan S Harrell
@ashtexas
When I was a kid, my parents worried about me. They sent me to a child psychologist, but I have to say, that kid didn’t help me a bit.
10:26 AM · May 9, 2012·Twitter Web Client
 
Google Books
That Self-Forgetful Perfectly Useless Concentration
By Alan Shapiro
Chicago, IL: The University of Chicago Press
2016
Pg. 169:
Some years ago I went to a child psychologist—if Henny Youngman had written this opening sentence, he would have added: “The Kid didn’t do a thing for me.”
       
YouTube
Bill Murray as Rodney Dangerfield’s Psychiatrist
May 14, 2018
Rodney Dangerfield
Throughout his career, Rodney told countless jokes about his good-for-nothin’ psychiatrist. In this sketch from his 1982 TV special, “It’s Not Easy Bein’ Me”, Bill Murray played the role of Rodney’s psychiatrist to a tee.
2:35
“For four years they sent me to a child psychologist. The kid didn’t help me at all!”
   
Twitter
Mr. Goodkat
@NathanDrakeXX
Replying to @Integrity_Guy
When I was younger my parents sent me to a child psychologist. That kid didn’t know what he was taking about.
12:51 AM · Feb 1, 2019·Twitter for iPhone
 
Twitter
8thlake
@intendtogether
“for four years they sent me to a child psychologist; the kid didn’t help me at all!” #dangerfield
Bill Murray as Rodney Dangerfield’s Psychiatrist
Throughout his career, Rodney told countless jokes about his good-for-nothin’ psychiatrist. In this sketch from his 1982 TV special, “It’s Not Easy Bein’ Me”...
youtube.com
6:08 PM · Apr 30, 2019·Twitter for iPhone
 
Reddit—Jokes
Posted by u/Flying_Milkshake November 26, 2019
When I was younger my parents sent me to a child psychologist
That kid didn’t help at all.