Make a Sorting Hat centerpiece. Cut a cone shape from a piece of 24x 18 purple poster board. Roll it into a cone and tape or staple it together. Cut out crescent moons and stars from yellow paper and glue on. Place a few stuffed owls around the party room. Make stars and lightning bolts from white poster board. Paint them silver and gold and use them to decorate the party room. Hang some from the ceiling, glue some to the walls and attach some to the chairs.
For older children, decorate the room with lit candles. Make place mats that represent the four houses of Hogwarts. Use plain white paper and the colors that correspond to each house. The house colors are: Slytherin-silver and green, Hufflepuff-yellow and white, Ravenclaw- blue and silver, and Gryffindor-scarlet and gold. Let each child choose a piece of paper from the sorting hat to determine which house they are in, and where they will sit at the party table. Be sure you have the same number of placemats and pieces of paper.
Serve Bertie Botts every flavor beans. You can either buy the Bertie Botts beans, or use Jelly Belly jelly beans. The Bertie's beans have some odd flavors, like grass and vomit. Make chocolate frogs by melting chocolate chips in the microwave, and dipping gummy frogs into the melted chocolate. Place them on wax paper to cool and harden. Keep them chilled until you serve them. To make a wizard hat cake, bake three or four round cakes of the same size. Stack the cakes, frosting between the layers. Cut the layers into a cone shape. Frost the whole cake with purple frosting. Decorate the hat with yellow star and crescent moons.