Well do you have a sand box ? How about kicking around a soccer ball ....Side walk chaulk? Can you make an obstacle course in your backyard? Or create a scavenger hunt .... How about going to your local home depot/lowes/rona and asking them to save you a big box say from a bathroom cabinet display flip it upside down and cut a door in it and they can make a ship/fort/cave? Set up a tent and let them pretend they are camping and pack them lunch to have out there. Generally I tell them to go play or I will find them something to do and guaranteed it won't be too much fun.