Water balloon toss (make extras and let them have a free for all afterward)
Running in Sprinkler or playing w/ water hose
Soccer, football, baseball, basketball, kickball
Science "experiments" - make your own goop, diet coke/mentos, make your own play dough, etc.
Movie Day with popcorn
frisbee "golf" (use hoola hoops for the holes - lay them flat or have the other kids hold them up)
hoola hooping contest with music
relay races - crab walk, bear crawl, egg on spoon (outside!), sponge relay (wet bucket at one end, dry bucket w/ fill line at the other end)
scavenger hunt or clue hunt - hide plastic easter eggs with clues to the next location - have a treat hidden at the end
Anything arts and crafts - my older ones love painting, bracelet making, and beading
Cooking - have them help mix cakes, cupcakes, cookies, make salad, squeeze ketchup into funny shapes or faces, make parfaits with yogurt and fruit, etc.
String bubbles with dish soap - makes HUGE bubbles
sidewalk chalk murals
....that's all I've got for now! Hope this helps.