Draw a bone shape on the foam sheet in pencil: a central rectangular bar with a small circle at each of the four ends, like a classic dumbbell. The whole bone should be about 6 cm long. An adult cuts this out cleanly with the craft knife.

Pour a thin, even layer of white paint onto the flat plate. Dip the foam stamp into the paint, covering the surface evenly. Do a test print on scrap paper: the bone should print as a solid white shape with clean edges. If it looks blobby, there is too much paint on the stamp; if patchy, add a little more.

Print bones across the bag front in a scattered, casual arrangement. Some can angle left, some right, some horizontal. Leave roughly 1 cm between prints. The bag is black so each white bone pops immediately.

Let the printed bag dry for twenty minutes. The paint will dry slightly raised on the bag surface, which gives a pleasingly tactile result.

Once dry, add a simple skull face in white paint using a round brush at the top of the bag if you want a full skeleton theme. A circle with two dots for eyes and a row of small rectangles for teeth takes about three minutes.