Wrap an empty matchbox with a printable cover (download at parenting.com). Glue a construction-paper road with handwritten party details inside. Glue a chocolate car (set of 60, $57; acandystore.com) on the road to finish
Suit the kids up in Blue Castle boilersuits ($17; amazon.com) or ask them to wear a shirt in their favorite race-car color.
Spray-paint paper boxes (free at copy stores) and let dry. Cut a slit in the top large enough for a child and bend a flap to make a windshield. Cut two small holes on each side and criss-cross two ribbons through to make straps. Tie to secure. Let the kids decorate with stickers, paper plates, markers, card stock, and dollar-store bike horns
Decorate cupcakes with racing flags (set of 144, $8; amazon.com).
Put a simple lunch in white gable boxes ($1; shopsweetlulu.com) adorned with card-stock paper tires.
In your backyard or at a nearby park, organize races so the kids can run and honk their horns while wearing the car costumes.
Pre-party, make a winner’s podium out of milk crates ($4; Target stores) and poster board. At the end of each race, call winners to the podium and hand them a trophy (set of six, $5; partycity.com).