The trouble began with the truck. We usually went to the playground with only snacks: water and some Cheez-Its or an applesauce pouch. But one day, my son wanted to bring a toy. So we arrived with his little yellow excavator truck, which he rolled in zigzags on the sidewalk and then used to dig up mulch and dump it back on the ground in a pile. He was 3, and suddenly the most popular child on the ...