She’s been photographed power-walking in TriBeCa with a personal trainer to work off the baby weight, but Mariah Carey gave into her cravings Tuesday, sneaking out for a late-evening snack at Midtown’s Sprinkles Cupcakes, spies say. When the songbird showed up at the cupcake mecca past 9 p.m., she found the place locked and the staff cleaning up. But they flung open the doors for the diva, and gave her a dozen red velvets to box up. Carey ordered a cup of milk to wash it all down (no word whether it was skim). Carey welcomed twins Monroe and Moroccan Scott in April, and has since been posting pics of herself jogging with her five dogs and working out in the ocean.