When I found them they were playing in a structure that had not previously been in our yard.
They had found a refrigerator box on the curb, unbeknownst to me. Apparently our neighbor's garbage is their treasure. They made a tank and were playing army soldier.
I don't know why Brian and I bother to buy the boys toys. They play with them for an hour or so and then the toys become dust collectors under their bed. Give them a box, however, and whamo...they're out of site all day.
I think I'm going on a box hunt soon. It's much cheaper and more fun. pow pow...