The lockers aren't part of some new museum campaign to entice the pistol-packing crowd toward culture. They're the latest outcome of the state Legislature's efforts to make children's museums and other public buildings and spaces safe for gun owners.
"I can't imagine why someone would feel the need to bring a gun to a children's museum," says Barbara Meyerson, director of the museum. "We've always seen this place as a bubble away from the outside world, where you can explore and challenge your imagination."
But state politicos have been blowing a different kind of protective bubble.
In recent years, they have diminished the authority of Arizona communities to keep weapons out of places like the Museum for Youth and other public buildings and parks.
"The Legislature has been delving into this area and making some fairly significant changes to the law," says Neal Beets, Mesa city attorney. "It seems that every session they add another subparagraph to it."
Before the recent changes to the statutes, which take effect this year, cities could legally keep firearms out of public buildings by posting "no weapons" signs in the lobbies.
The Mesa museum had one at its front desk.
"That seemed to work just fine," says Meyerson. "As far as I know, we've never had anyone come in here with a gun, so it's never been an issue."
Occasionally, perhaps five or six times a year, someone tries to bring a gun into the Mesa city library. "For some reason, libraries seem to have more experience than city hall does with patrons showing up with six-shooters," says Beets.
Gun toters show up even less frequently at Tempe, Scottsdale and Glendale libraries.
"In the 11 years that our new library has been open," says Will Manley, city manager of Tempe, "we have never been asked to store a gun."
Yet Phoenix library officials say the city's libraries, particularly the central branch, have been hosting armed readers on a regular basis for a number of years.
Previously, state law allowed guards at libraries and other government buildings to simply ask gun toters to either leave their guns at home or put them in their cars.
But last year's legislative tinkering stripped cities of that option.
"One of the things that that legislation made clear," says Marvin Sondag, an assistant city attorney for Phoenix, "was that we could prohibit people from bringing guns into our buildings only if we provided a means of advising them that weapons were prohibited and then securing the weapons for them."
This change affects not only government buildings. City buses can no longer prohibit people from bringing loaded weapons on board. And city parks that ban guns also have to provide storage.
Tempe plans to continue its policy of having armed visitors park their weapons at the downtown police station, which is just a block from most city offices, or with security guards at outlying facilities.
"If the site doesn't allow that," says assistant police chief Jay Spradling, "we will send a police officer out to take the weapon."
He says it didn't make sense to spend money for lockers that won't be used very often.
"When we were looking at them," he says, "we were looking at several hundred dollars for a two- or three-bank locker. If it's an open environment, where the public has access, it has to be a pretty secure thing."
Mesa is spending about $2,500 for 50 pistol boxes. Glendale is shelling out about $1,700 for 48. Phoenix, which already has some self-serve lockers in place at its central library, has bought about 235, for $7,000. None will be bulletproof.
The change in state law emerged as a compromise on a bill that would have eliminated the power of Arizona municipalities to enact and enforce laws governing anything related to firearms and ammunition.
The National Rifle Association and other pro-gun groups, such as the Arizona-based Brassroots, Inc., have been pushing for such bans -- called pre-emptions -- on the enactment of local gun laws. That effort is part of the NRA's effort to undercut gains that gun-control forces made in the 1990s, both at the federal and city levels.
In the past decade, about 40 states have passed partial or total pre-emptions.
"Clean pre-emption is what we're after," says Gary Taylor, president of Brassroots. "Arizona is real close to that right now, but there are still a lot of ifs, ands or buts in the law."
Taylor describes his group as "a no-compromise organization. We're not willing to throw legislation out on the table and then whittle it down."
His organization backs the NRA's recent fight against the city of Tucson's efforts to regulate gun shows at city facilities. It previously opposed, unsuccessfully, Tucson's ban on carrying weapons in city parks.
He'd like to see the federal ban on guns at schools repealed, but doesn't think that'll happen.
Last fall, Brassroots began warning Valley libraries that they were preparing to test the new laws.
"They called us," says Manley. "We were ready for them, but they never showed up."
About 30 members of Brassroots did arrive, fully loaded for book, at Glendale's library.
"Most of them were dressed in white shirt and tie," says Jerry McCoy, a city spokesman, "but one guy showed up in hunting fatigues and had a hunting rifle. He attempted to get into the library and he wanted to know why he couldn't walk in with his hunting rifle."
"Call me conservative," says McCoy, "but I would be willing to bet that most of our library patrons would not want to see weapons strapped around people's belts in the library. And we have not received any requests for securing weapons except from this group. That's in a town of 220,000."
Taylor says he just wants Glendale, Mesa and other Arizona cities to abide by the new law.
"As long as they're making an attempt to do that, we'll leave them alone."