When the app starts, press to move over to ‘Library’ and select ‘Interactive Episodes’.
This is unlocked in Episode 2, ‘Baby Bear’s Baby Doll’, Chapter 7, ‘Elmo’s World: Beach’.
At one point in the chapter, many things will appear on the screen for you to “touch”. When you are standing on the beach, a number of pails and beach balls and some other things will appear. Keep hitting them with your arms and legs and they will be knocked off the screen.
The simplest way to unlock this achievement is using ‘Chapter Select’ to choose the chapter. When the chapter is over and the next one starts, just press , move over to ‘Stop’ and press again. The achievement will unlock when it is buffering. You can alternatively watch the entire episode, but that would be more time consuming.