When First Lady Michelle Obama makes an announcement today about marketing healthier foods to children, she'll be accompanied by the popular Sesame Street characters Elmo and Rosita--and the less well known, albeit more powerful, representatives of the Produce Marketing Association, a trade group, and Partnership for a Healthier America, a nonprofit founded by Obama herself, which has strong corporate support.

The announcement comes on the heels of an industry summit and major speech Obama gave in late September, in which the first lady made her  strongest statement in recent years about advertising practices aimed at children. "You know that ...