Open a tub of playdough and separate it into 7 or 8 smaller pieces.
Roll each chunk of playdough into a long, skinny "log".
Blow up a balloon and then let it deflate. This stretches the latex (or rubber) and makes it easier to fill.
Using four fingers, stretch open the mouth of the balloon.
Have a little helper add the rolls of playdough, one at a time.
Push the playdough down as far as you can into the balloon as you add each "log".
When you've added the full tub of playdough (but before you've removed your fingers from the balloon), push the playdough down so it's out of the neck of the balloon.
Push all the air out of the balloon and tie a knot in it, as close to the playdough as possible.
Cut off the excess balloon neck.
Have fun squeezing and stretching the playdough stress ball.
Your playdough stress ball is complete!
Video
Notes
An adult will likely need to stretch open the neck of the balloon (it takes quite a bit of strength!).