How will the kids make the letter X out of playdough? Some might make two "sausages" and cross them over - as if they were writing the letter.
Alphabet Decorate The Letter X Playdough Mat Lower Case
Why not make working with playdough one of your "letter of the week" activities - and print out this playdough mat, for the letter X, to help!
I'm not sure how you model an X-Ray out of playdough - but perhaps the kids can come up with a way? You might relax the rules with this playdough mat and ask them to model words ending with the letter x, too.