Party Idea: Trucks and Dirt
This party works best outdoors. All you need is a mound of dirt or play sand (or a sandbox, if you've got one). Cover the dirt or sand with toy people and animals -- just make sure none of the objects you choose pose a choking hazard -- and an assortment of toy dump trucks, cranes, and plows. If it rains, forget the dirt and move trucks and objects indoors. Kids will love pushing and carting around their miniature cargo on the living-room floor.
Make cleanup easy by having kids remove shoes and socks before they get in the dirt or sand pile, and have a hose or large watering can nearby for rinsing hands and feet.
To extend the theme, gather all your riding toys (or borrow some from the neighbors) and designate a "driving" area, marked off with chalk. You may be surprised how popular an activity this is. Be sure to have an adult monitor, so the children will take turns.
Make a "dirt" cake with chocolate crumbles (crushed Oreos work well) or a "sand" cake with smashed vanilla wafers.