The escalating war on junk food in schools has targeted a new enemy -- that gooey, sugary, and often irresistible sandwich spread known to children everywhere as Fluff. Outraged that his son was served peanut butter and Marshmallow Fluff sandwiches at a Cambridge elementary school, state Senator Jarrett T. Barrios , a Democrat, said he will offer an amendment to a junk-food bill this week that would severely limit the serving of marshmallow spreads in school lunch programs statewide. ``A Fluff sandwich as the main course of a nutritious lunch just doesn't fly in 2006," Barrios said. ``It seems a...