“What do sweet potatoes wear to bed?”/“Their yammies.”

A sweet potato riddle is:
 
Q: What do sweet potatoes wear to bed?
A: Their yammies.
 
The “yammies”/“jammies” (pajamas) joke has been cited in print since at least 2002.
     
 
Google Books
Collect-N-Do Object Talks for Kids
By Susan L. Lingo
Cincinnati, OH: Standard Publishing
2002
Pg. 32:
Cut the index card in half and write the following riddle on one half of the card: “What do sweet potatoes wear to bed?” Now write this answer on the other card: “Their yammies.”
   
Twitter
Lindsay Keeping
@lindsaymrk
What do sweet potatoes wear to bed??
9:39 PM - 25 Nov 2009
   
Twitter
Sushi Ed
@SushiEd
What do baby sweet potatoes wear to bed? ♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥♥ Their YAMMIES!!!!  (C’mon - let that laugh out.)
10:57 PM - 24 Mar 2010
   
Twitter
Erica Osuna Johnson
@osunae
What do sweet potatoes wear to bed???        their yammies   :p
3:44 PM - 25 Nov 2010
   
Twitter
Calley
@Calleygator
What do sweet potatoes wear to bed?
Their yam-mies #jokeoftheday
1:53 PM - 14 Sep 2017
 
Twitter
dad jokes
@dadtellsjokes
What do sweet potatoes wear to bed?
Their yammies
10:51 AM - 23 Apr 2018