Purchase a large piece of corkboard with a vinyl coating on the back. Draw the shape you want your headboard to have with a piece of chalk. For example, a standard rectangular headboard for a child's-size bed is 41 inches by 45 inches, but your headboard can be any shape or size you like.
Cut out your headboard shape with a jigsaw. Measure a piece of foam and piece of batting that are both 3 inches longer and wider than the shape of your headboard. Cut them out with a pair of shears or some utility tape.
Lay the piece of foam facedown on a flat surface. Place the headboard on top of the foam, also facedown. Place the sides of the foam taut against the back of the headboard. Staple them in place with a staple gun. Repeat with batting.
Select a flat sheet that depicts one of your child's favorite fictional characters. Cut it to the same dimensions that you cut the foam and batting.
Place the sheet facedown on a flat surface. Place the side of the headboard that's covered with foam and batting on the center of the sheet that's facedown. Pull the sides of the sheet against the back of the headboard and staple in place. The headboard is now ready for mounting to the wall.