Alexandra Sierra carried boxes of food to her kitchen counter, where her 7-year-old daughter, Rachell, stirred a pitcher of lemonade. “Oh, my God, it smells so good!” Sierra, 39, said of the bounty she’d just picked up at a food pantry, pulling out a ready-made salad and a container of soup. Sierra unpacked the donated food and planned lunch for Rachell and her siblings, ages 9 and 2, as a reporter watched through FaceTime. She said she doesn’t know what they’d do without the help. The family lives in Bergen County, New Jersey, a dense grouping of 70 municipalities opposite Manhattan with about 950,000 people whose median household income ranks in the top 1 percent nationally. But Sierra and her husband, Aramon Morales, never earned a lot of money and are now out of work because of the pandemic. The financial fallout of COVID-19 has pushed child hunger to record …