KEEP THE KIDS off the street. They could get hurt out there. And anyway, it's more fun playing on the sidewalk.
Collect and clean plastic squirt bottles (detergent, catsup, syrup, whatever). Fill with water and hand them out with directions to "make a design on the sidewalk." They'll be busy for hours, and evaporation will constantly renew their canvas.
Buy a couple of pieces of the chunky chalk found at building supply, hardware or art stores. Regular blackboard chalk will do, especially the colored kind. Tell the kids to make a picture on the sidewalk or driveway. If they use the driveway, put up a big barricade no driver could overlook.
When they get tired of drawing, have them trace around one another's shadows with the chalk. Then have them trace shadows of the tree, bush, house, light, whatever, at different times of the day. Mark the shadows with the time. How do they change through the day?
Teach them how to play shadow-tag. The child who's "It" tags other children by stepping on their shadow.
WAIT AND SEE --
This requires eyedroppers, which can be collected throughout the year or bought cheaply at the drugstore, and plastic cups. Fill the cups with a variety of solutions: salt water, sugar water, epsom salts, coffee, lemonade, soda pop, milk . . .
Have them place drops of the various solutions on the sidewalk, then wait and see. (Outline and label the spots with chalk, to keep them from getting lost, mixed up or stepped on.) What becomes of the drops? Which attract insects, and what kind? Which dries fastest? Which stays wet longest? Attention spans, or the lack of them, can be a problem here on a cool day.
Give children a variety of different types of paper -- tissue, computer paper or lightweight paper bags -- and crayons. They can then make rubbings of different textures found around the house, yard, and on the sidewalk. Hold the paper over a surface, rub with crayon until texture is revealed.
GIANT STEPS --
Draw "start" and "finish" lines on the sidewalk. "It" stands behind the finish line and gives commands such as "two baby steps," "one baby step," "one giant step" or "three hops." The players do what they're told, but also try to creep up without being caught. If "It" catches someone moving, that child goes back to the start. The first one to reach the finish line is the new "It."
Regional variations of this game include "Simon Says" and "Mother, May I?" And once the kids get started drawing lines, they'll soon go on to improvise infinite variations of tic-tac-toe and hopscotch.