Milwaukee transit bus driver Cecilia Nation-Gardner immediately suspected trouble when she saw a young girl wandering aimlessly along a busy street crying in her pajamas and slippers on a hot muggy morning in July.

She didn't see a caretaker around so she pulled over to talk to the 6-year old who told her she was trying to find her mother who lives in Georgia. She then asked the child to board the bus while she called authorities. Minutes later, the girl’s panicked family arrived and took her home.

This was the second time Nation-Gardner had rescued a lost child. In May, she spotted a young child running into traffic after he wandered away from school.

“Had it not been me, had it been a sex trafficker or child molester, that’s the only thing goes through my mind in those situations,” Nation-Gardner, 54, told NBC News. “As a bus driver, you have to be attentive to everything going on around you.”

Less than four hours earlier on the same July day, a toddler was found by another Milwaukee public bus driver, Cressida Neal, 47, at 4 a.m. after the child wandered away from his grandmother's house in the middle of the night.

“I’m glad I was in the right place at the right time for that child,” she said.

At least a dozen lost kids — most under the age of five — were found and safely returned to their families by Milwaukee County bus drivers since 2016, according to the Milwaukee County Transit System.

While there is no national data tracking how many lost kids are found by bus drivers, those working in public transit advocacy say the Milwaukee bus drivers' actions are emblematic of what bus drivers across the country do each day: act as the eyes and ears of the community and come to the aid of those in need of help.

"It’s not just lost kids that bus drivers end up helping," said Polly Hanson, senior director of security, risk, and emergency management for the American Public Transportation Association. They come to the aid of seniors with dementia, disoriented adults and even crime victims, she said.

For so many people, buses are a safe space because of the drivers, she added. “Bus operators are the unsung heroes that make communities safer.”

Last month, a Dayton area transit bus driver spotted a 4-year old boy running in the street and called police after getting the child on board. The boy had gotten lost after leaving his yard through an unlocked gate, according to WHIO-TV Dayton.

A New Jersey Transit bus driver quickly came to the rescue of a pedestrian who was struck by a car in April by calling 911, creating a safety perimeter around the victim, and waiting until first responders arrived.

Several transit bus systems have even begun training drivers on spotting human trafficking victims, including in Pasco County, Florida where dozens of drivers have already become watchdogs for law enforcement.

But while they are tasked with these de facto roles of looking out for others, they are not always respected, Hanson said.

According to Federal Transit Administration data, bus transit systems reported over 500 more worker injuries in 2016 than in 2008.

“Bus drivers go over and beyond all the time but being a bus driver is a really hard job. And it can be very dangerous because we deal with a lot of different people,” said Nation-Gardner. “We do what we have to do, but there is always a risk.”

Several attacks on bus drivers have taken place just this year.

In May, a bus driver in Tampa, Florida, was stabbed to death by a rider on the HART's MetroRapid line, one of the system's most heavily traveled north-south routes, in May. The suspect argued with the operator before attacking him, authorities said.

A Seattle bus driver navigated his bus with about 12 passengers on board to safety after he was shot by a gunman who also carjacked two vehicles. The driver survived the attack and was hailed a hero for detouring the bus out of harm's way despite being shot himself.

“Bus drivers are charged with a lot of responsibility,” said P.S. Sriraj, director of the Urban Transportation Center at the University of Illinois at Chicago.

Drivers are on the hook for so many things including keeping schedule, he added.

While going out of your way to help others is commendable it can sometimes come at the cost of efficiency. “If you’re a public transportation operator you’ve got to keep schedule in order to ensure trust between you and fare-paying customers. The moment you step out of bounds to help a child that trust is jeopardized.”

If the driver is able to rescue kids while at the same time doing what they're paid to do, they have to be really commended, he added.

For Nation-Gardner, she feels what she did for those kids was part of her job not only as a bus driver but as a human being.

"Everybody is calling me a hero, I don't consider myself a hero. I consider myself a woman that believes in God, and God always puts me where I need to be at the right time."