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Every summer across the country, more than 3 million children eat for free at more than 30,000 sites, from schools to recreation centers to migrant worker camps.

It's a valuable resource for families who are struggling -- but, critics say, a convenient freebie for those who aren't.

At the "Summer Fun Cafe," which Fox News visited in northern California, and others like it, meals are funded by the U.S. Department of Agriculture provided at least half the children in the area qualify for free lunches during the school year.

But come summer, anyone 18 and under can pull up a chair to Uncle Sam's table.

"There's no income requirement, no enrollment, no paperwork," said Monique Stovall, nutrition director for the San Juan Unified School District outside Sacramento. "All children in the community in that age range can come eat with us for free."

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Signs around the district headquarters advertise the fact that there is no eligibility requirement, and invite all kids to take advantage.

That's why, along with a choice of sandwich, fresh fruit, and milk, these free summer lunches come with a side of controversy. Critics wonder if the "come one, come all" invitation could have taxpayers feeding any child, whether they're needy or not.

Taxpayer watchdog groups say most Americans are fine helping children truly in need.  But Jon Coupal with the Howard Jarvis Taxpayers Association asks: "If someone is coming from a family that makes a quarter-of-a-million dollars a year, and they're not checking eligibility when they're coming in the door, I think most people would wonder, 'Am I paying for this?'"

For many low-income families, a free lunch means more money can go toward other meals or necessities. For those who can afford to feed their children, it's an easy way to get fed and go.

"Normally we wouldn't qualify for a free lunch, but we're close and it's convenient, and my kids like it -- that's important," said mom Julie Marks, who brought her two young boys.

In many cases, charity and nonprofit groups help sponsor free meal sites in their community. According to program supporters, the summer lunch program is easier to administer when the location qualifies, as opposed to the user.

"We don't have to ask your income, because the overall purpose of the program is to provide a healthy meal to children," Stovall said.

Organizers contend after a summer of nourishing meals, these kids will do better when school resumes in the fall. Monitors are on hand to make sure that the lunch is eaten on site, and that the adults don't mooch off the kids.