Create your own birthday centerpieces by making characters out of Styrofoam that match the theme of your child's party. Your character Styrofoam centerpieces can be anything you want them to be, even if you choose different characters for each table. It may be easier to begin by creating characters or shapes with sharper angles.

Determine how large you'd like your centerpiece characters to be. Select Styrofoam blocks that are larger than your design plans.

Gather pictures of each character you wish to sculpt into a Styrofoam character. Use coloring books or print images from the Internet. Have the pictures blown up at a copy center if you want larger sculptures.

Cut out your character and tape it onto the Styrofoam block, leaving 2 to 3 inches on the bottom to create a base for your character and increase stability. Draw the outline of your character directly onto to the Styrofoam, taking care to not press down so you don't mar the Styrofoam, and use a ruler to outline your base. Remove the picture of the character.

Use your long knife to carefully cut away the large excess chunks of Styrofoam; cut only the long lines or defined corners, then cut out the details using the short knife. Your knives should be sharp. Avoid pressing too hard or forcing the knives, as pieces of the Styrofoam may break off, ruining your character sculpture.

Gently brush off any excess beads of Styrofoam using a clean, soft paintbrush. Use your black marker to draw any outlines, such as the character's face, to help paint. Draw a back on one side or draw the face of the character on both sides if you'd rather have the face visible from any angle.

Paint your character in the colors you desire using craft or acrylic paints and soft brushes. Use a dabbing method to avoid inundating the Styrofoam with paint.