Three weeks before he was elected president, Barack Obama set an audacious goal: end hunger among children in the United States by 2015. Since his inauguration, Obama has seldom broached the subject. His aides brainstorm weekly with several agencies, but their internal conversations so far have not produced fundamentally new approaches. The president's goal could prove daunting: Childhood hunger is more complex than previously understood, new research suggests, and is unlikely to be solved simply by spending more money for food programs. If Obama intends to erase childhood hunger, the government will need to reach even further into the rowhouse kitchen where Anajyha Wright Mitchell sometimes takes tiny portions so her mother will have more food. 'I tell her to eat, eat, eat, because she is real skinny,' Anajyha, 12, said of her mother, Andrea Mitchell. Anajyha, a serious girl with two younger brothers and a mother who has lost two of her three part-time jobs, is growing up with an ebb and flow of food typical of a growing number of families. In her home, in a scuffed neighborhood called Strawberry Mansion a few miles north of the Liberty Bell, food stamps arrive but never last the month. There can be cereal but no milk. Pancake mix and butter but no eggs. The intricacy of the problem -- and of the Obama administration's task -- plays out here, where Anajyha could have enough to eat but shortchanges herself. Philadelphia offers a particularly vivid ground-level view of what researchers call a 'silent epidemic' of hungry and undernourished youngsters. For years, local civic activists, health experts and politicians have tried some of the nation's most innovative experiments -- and learned how intractable hunger can be. Researchers here have also been at the leading edge in trying to fathom the effects of a scarcity of food. Even when children are not hungry, studies have found that slight shortages of food in their homes are associated with serious problems. Babies and toddlers in those homes are far more likely to be hospitalized than children in families with similar incomes but adequate food. School-age children tend to learn and grow more slowly, and to get into trouble more often. Teenage girls are more prone to be depressed or even flirt with thoughts of suicide. Solving the problem is further complicated by its subtle nature. 'Most people who are hungry are not clinically manifesting what we consider hunger. It doesn't even affect body weight,' said Mariana Chilton, a Drexel University medical anthropologist who is part of Children's HealthWatch, a network of pediatricians and public health researchers in Philadelphia and four other cities. Hunger cannot be solved by food alone, their work shows, because it is one strand in a web of pressures that trap families, including housing and energy costs. This more nuanced picture is emerging as the problem has become more widespread. With the economy faltering, the number of youngsters living in homes without enough food soared in 2008 from 13 million to nearly 17 million, the Agriculture Department reported last month. In Philadelphia, researchers found that, during the first half of this year, one in five homes with a baby or toddler did not have enough food. And one of every dozen young children was outright hungry, a rate twice that of the same period the year before. Although the problem has deepened, White House and Agriculture Department officials say the president's goal remains, as one put it, 'something that seems manageable.' Congress increased food stamp benefits this year by $20 billion and, more recently, set aside money to test ways to feed children when school is out for the summer. The president's aides are focusing on a congressional debate, deferred from this year to next, on how to renew the nation's main child nutrition law. Although ideas in Washington have not fully crystallized, an unlikely lobbying force is at work. A group of Philadelphia women has begun appearing on Capitol Hill and at national conferences as part of a 'Witnesses to Hunger' project, organized by Chilton, who handed video cameras to 42 mothers to document their efforts to feed their children. But learning to dress for success at news conferences, these women are discovering, does not solve the food problem at home. One of the 'witnesses' is Christina Koch, whose younger son Jesus, 2, wakes up at night thirsty for milk or juice. 'If I don't have it,' she said, 'I take him into bed and try to rock him to sleep.' Running out of drinks for her toddler is part of a tangle of obstacles that shape Koch's days. At 26, she lives in North Philadelphia with her son, Dale, 5, a picky eater, as well as Jesus and her fiance, Jesus Nieves, who has had as much trouble finding and keeping jobs as she has. Not long ago, when she had the money, Koch bought more than 20 boxes of macaroni and cheese and stored them under her kitchen sink. The sink leaked. Every box was ruined. For the past few months, the gas and electricity have been cut off because she hadn't paid the bills. She has been cooking on a hot plate, borrowing electricity from the neighbor in the rowhouse next door, who let her thread a jumbo extension cord through the kitchen window. But when the neighbor was evicted last month, she was down to using candles until her family chipped in to pay her bill. She is bad, she knows, at budgeting. In early November, when $650 in food stamps came, she splurged on $18 in Chinese takeout. When the food stamps run out, she buys on credit from Indio's Mini Market, a few blocks away. In October, she ended up with a $300 tab. Koch met Chilton, the anthropologist, in the emergency room at St. Christopher's Hospital for Children, where Chilton and her co-workers spend hours on questionnaires to measure the food shortage. Across the hospital parking lot is the GROW clinic, which provides more evidence of the effort it takes to make a difference, even a few children at a time. Inside the clinic -- similar to Children's HealthWatch clinics in Baltimore, Boston, Little Rock and Minneapolis -- pediatrician Hans Kersten and a team see about a dozen young children and their parents each week. Four in five children here and at the other sites are not getting adequate food. The team checks head circumference as a clue to brain growth, motor skills, toddlers' vocabulary. 'Hi, beautiful,' nutritionist Kristen Roscioli says as the team walks into the examining room where 14-month-old Joeanna, the first child of Sherita Parks and Joseph Mouzon, is waiting in a diaper and pink barrettes. 'She has managed to gain about two pounds, which is great,' Kersten tells Joeanna's parents. 'But she still is underweight?' Parks asks. 'She is a tiny girl,' he replies. 'We just want her to be healthy.' The main problem, her parents say, is that Joeanna doesn't like to eat. But Parks also says, 'It would be great if we could get food stamps.' Mouzon's pay from working in a pharmaceutical warehouse means they just miss qualifying. 