Cash-hungry states and municipalities, in pursuit of even the smallest amounts of revenue, have begun to exploit one market that they have exclusive control over: their own property.

With the help of a few eager marketing consultants, many governments are peddling the rights to place advertisements in public school cafeterias, on the sides of yellow school buses, in prison holding areas and in the waiting rooms of welfare offices and the Department of Motor Vehicles.

The revenue generated by these ads is just a drop in the bucket for states and counties with deficits in the millions or billions of dollars. But supporters say every penny helps.

Still, critics question whether the modest sums are worth further exposing citizens — especially children — to even more commercial pitches.

“I have a 5-year-old who doesn’t understand what ads are,” says Megan Keller, 30, of Provo, Utah, who says her son Collin, a kindergartner, sees seductive posters for sugary cereals every day in the lunchroom of his public school. “I don’t like that he thinks, ‘Oh, this is good because it comes from my school,’ and I’m having to explain to him why that’s not true.”

Because Utah will soon start selling ads on the sides of school buses, Ms. Keller has decided to transfer Collin to a nearby charter school that has sworn off commercialism.

Utah became the latest state to allow school bus advertising when its governor signed a lawlast month authorizing the practice. The strategy began in the 1990s in Colorado, then spread to Texas, Arizona, Tennessee and Massachusetts. In the last year, at least eight other states have considered similar legislation.

One of them, New Jersey, approved school bus advertising in January, and the state’s Board of Education is now writing guidelines for size and sponsorship restrictions. So far, four districts have expressed interest in participating, according to Frank Belluscio, a spokesman for the New Jersey School Boards Association. Idaho’s Legislature rejected a similar proposal earlier this month.

Districts with 250 buses can expect to generate about $1 million over four years by selling some yellow space, according to Michael Beauchamp, president of Alpha Media, a company based in Dallas that manages advertising on 3,000 school buses in Texas and Arizona.

Officials say that the revenue, while small, can still make the difference between having new textbooks — or a music teacher or a volleyball team — and not having them.

“If the alternative is huge classroom sizes and losing teachers and losing qualified personnel, yes, this seems like something we should consider,” said Valery Lynch, 48, a fourth-grade teacher in The Woodlands, Tex., north of Houston. “But I know that it’s a bag of worms, and people are going to ask ‘What’s next? An ad on the classroom clock?’ “

Some schools have been selling advertising space on their school Web sites and in campus parking lots, in addition to the lunchroom and the school buses. An online ad usually generates about $100 a month for a school, according to Jim O’Connell, the president ofMedia Advertising in Motion, a company in Scottsdale, Ariz., that sells advertising for school districts.

Critics say exposing impressionable young children to ads that appear to be endorsed by their educators is problematic.

“Mandatory education laws are based on the idea that education is good for society, and is good for kids,” said Josh Golin, associate director of Campaign for a Commercial-Free Childhood, a nonprofit organization. “That argument falls apart when you’re talking about mandatory exposure to advertising.”

The companies that help place the ads say that children are exposed to advertising just about everywhere they look anyway, including — for many decades — in their high school yearbooks and sports stadiums. They say that the primary audience for ads on the outside of school buses is adults, not children, and that much of the space is being purchased by dentists, banks and insurance companies.

“School bus advertising is not for the kids in the bus, but for the cars around the bus that see the advertising when they’re at a stop sign or driving down the highway,” said Bryan Nelson, a Republican state representative from Florida’s 38th District, outside of Orlando. Mr. Nelson is sponsoring legislation that would allow school bus ads and direct much of the revenue toward defraying the buses’ fuel costs. “When you think about how many people are going to see those ads, you get a lot of exposure, so we can charge a premium price,” he said.

Some states, including Florida, already allow advertising inside the bus. And while many states have prohibited school bus advertising for alcohol, tobacco and sexual content, none have ruled out displaying ads for junk food, Mr. Golin said.

Pizza parlors and pizza chains are among the businesses that have purchased advertising on school buses.

“When concern about childhood obesity is at an all-time high, and there’s a focus on taking junk foods out of schools, it’s still possible to see ads for those very same products on the sides of school buses,” said Mr. Golin. “It makes no sense.”

In addition to schools and school buses, jails are also getting ads in some states and counties.

Who would want to advertise to criminals? Defense lawyers and bail bondsmen.

Next week, Erie County Holding Center in Buffalo will begin displaying ads on new high-definition television screens that defendants see immediately after arrest. The spots, which run on a loop along with the informational messages from the holding center, sell for $40 a week and have nearly sold out for the rest of the year.

Anthony Diina, president and owner of Metrodata Services, the private company hired to run the new system, said he expected the program to bring the county $8,000 to $15,000 a year. The governments of Alaska, San Francisco and Orlando, Fla., have also contacted his company about setting up advertising programs in their jails. A jail in southwestern Florida started a similar program in 2009.

Last year, Mr. Diina’s company set up television screens for advertising at the Erie County offices of the state Department of Motor Vehicles, a pilot program that he expects to bring the county revenue of “six figures over the course of five years.” He says that the reaction so far has been positive.

“These ads provide distraction and amusement that lessens the perceived waiting time,” Mr. Diina said. “And it doesn’t hurt that they bring in some money, too.”