Pediatrician Randy Christensen's office is a Smurf-blue RV called the Crews'n Healthmobile that children can see coming from blocks away. Some visit with their families, while others come alone, making the trip from shelters or while wandering the streets — or emerging from their makeshift homes in boxes, under bridges, or even in holes and culverts dug in the ground.

A staff member at Phoenix Children's Hospital, Christensen started Crews'n in 2000 and now spends all of his clinical time there. The mobile clinic treats homeless and at-risk infants, children and adolescents up to age 24. There are two RVs, one that motors to sites around Phoenix and a "fixed-site" vehicle parked at a family shelter. Inside is a state-of-the-art pediatrician's office with multiple exam rooms and an electronic health record system.

All told, Christensen and his 10-person team host 15 half-day clinics each week. Phoenix Children's provides 40 to 50 percent of the $1.2 million a year funding for the operation as well as grant-writing assistance.

The need is great: On any night in Arizona, says Christensen, an estimated 5,000 to 10,000 homeless kids are on the street, yet only 500 shelter beds are designated specifically for them.

Christensen and his staff treat clinic patients for everything from the flu to STDs, bone breaks and diabetes. They also administer prenatal care and provide some mental-health services.

The illnesses tend to be more advanced than most general pediatricians encounter. "If it's an ear infection, it's probably not an ear infection that happened that day," says Christensen. "It's probably one that they haven't been able to do something about for a couple weeks. So, you look inside and the eardrum is perforated. Or, you might see somebody with an arm that's been broken for two days. And you ask, 'Why didn't you go to the hospital?' [The answer is,] 'Well, we don't have any insurance.'"

The clinic works closely with the hospital to provide referrals. "We've had kids with cancer, with kidney failure; we've had all kinds of issues and Phoenix Children's takes care of them," he says.

Christensen not only provides a "very high quality of care;" he also has a great rapport with the kids, many of whom he's seen repeatedly, says Albert Jacobson, M.D., division chief of the Children's Medical Group at the hospital.

"Children in situations where they're homeless and in shelters don't have a lot of trust," says Jacobson. "He's been able to build that up."

Christensen has worked with homeless children for almost his entire career. While a resident at Phoenix Children's Hospital, he started a clinic at a school for homeless children.

Around the time he completed his residency, the agency that ran the school landed a grant for $460,000 to launch a mobile clinic. They asked Christensen to be the medical director.

There was one catch: They couldn't pay his salary. He talked his supervisor at Phoenix Children's into letting him spend some of his time on the mobile unit, and by 2009 he was able to work there full time.

At first, the Crews'n staff consisted of just Christensen and a nurse practitioner. "We learned how to do things along the way, had a lot of setbacks, made a lot of mistakes, and just kept at it until we finally got it right," he says.

Around 2009, with the economy in the dumps, things got harder. Partner agencies that were helping patients with things like bus passes and food shut down. "We're having to rethink our budget as well," says Christensen, noting that the clinic no longer pays for X-rays and has slashed its pharmacy expenses. And, they laid off a nurse practitioner trained in psychiatry who ran the clinic's mental health program.

"It was working so well," Christensen laments. "These kids who had huge amounts of mental-health diagnosis were coming to see us. They were taking their medicine. And then, all of a sudden, that agency no longer had the funds," due to federal budget cuts.

But he's working on writing grants to restore that money. "Next time, we'll make sure we're the recipients of those federal dollars," he says.