Higher- and middle-income households spend the second-most on child-care and education, followed by food, while nutrition was a bigger share of expenses for poorer households, with more lower-income families caring for their children at home, the study said. Transportation was the third-biggest expense across all income categories.

Costly services are making day care unaffordable for some low-income families, said Michelle McCready, a senior policy adviser with Child Care Aware of America, an Arlington, Virginia, group that advocates for government aid to poorer households. Those families rely on unregulated facilities or relatives to care for children, or in some cases give up jobs to raise them, she said.

“Parents do the math and either stay at home or go with unregulated care,” she said.

Lower-income families also are struggling more to cover food costs, according to government data. Enrollment in the Supplemental Nutrition Assistance Program, known as food stamps, reached a record 47.8 million people in December 2012, and annual spending has doubled since 2008. With children representing 45 percent of all recipients, the program has become crucial for lower-income families with children, Concannon said.

Housing Costs

Housing has covered almost a third of costs to raise a child since the first study. The real-estate market collapse beginning in 2007 helped constrain cost increases, easing budget pressures for some families, said Mark Lino, the USDA researcher who wrote the report. A rebound, while healthy for the broader economy, may actually make home affordability more difficult for some families, he said.

“Health-care and child-care costs have been stresses to families over the past few years” more than housing has, Lino said in an interview. And while depressed property values lessened some strains, “falling home prices created their own sets of problems,” he said.

Low-income households have less to spend on personal-care items, entertainment such as video games or sports equipment, and reading materials, as basic necessities take a greater proportion of incomes. Since 1995, the lower third of households increased such miscellaneous spending by less than 1 percent, a decline in real expenditures when inflation is considered, Lino said. Spending on such items in wealthier homes rose 37 percent.

‘Cover Necessities’

“It’s a zero-sum game, and the bottom third has had to shift money to cover necessities,” he said. “The upper-income families have more flexibility.”