Fun Kid Activity: Lines of Colored Tape, straws and pompoms. Try straws and cotton balls. Adding the lines ups the challenge. Using pompoms allows you to adjust the size from tiny to pretty big. The pompoms are also nicer looking.
Paper Airplane Target practice -- yes! Cut holes in a large piece of paper and have children aim their hand-made paper planes through. Set a certain number of tries, and give a prize to the winner who got the most planes through the holes.