Fill one bowl with water and leave the second empty, both on a towel.
Show how to soak the sponge, lift it across and squeeze it out into the empty bowl. Then hand it over.
The goal is to move all the water. Expect drips everywhere — the towel is why they do not matter.
Squeezing a wet sponge demands sustained whole-hand grip strength, which is what lets a child later hold a pencil without their hand tiring. A clear goal — empty one bowl, fill the other — keeps them repeating it long past the point they would repeat an exercise.