But maybe think twice before taking them as authorities on complex environmental and economic matters.

The used lunch trays Emily Fox took home about four years ago from the loading dock outside her elementary school were gross, some still plastered with ketchup. Emily stacked the trays in piles of 10. She wanted to know just how many polystyrene lunch trays Piney Branch Elementary School students went through in a day.  “Three hundred and twenty-five,” said Emily, now 12…

On Friday, the Hermosa Beach City School District in Southern California started replacing foam trays with recycled paper trays once a week, thanks in part to the advocacy of Max Riley, a fourth-grader at Hermosa Valley School, and his sister Reece, a second-grader.

“No Foam Friday” will run through the end of the school year, and the siblings say they’re pushing for permanent change.

Max said he worries about the health repercussions of littering Earth with foam.