Susan Cole wanted to fly her 12-year-old son Danny from their Maryland home to Houston so he could catch a football game with his dad, who was there on a business trip.

Danny had only flown once or twice, and never alone. So Susan, plenty nervous herself, last month took Danny to Baltimore-Washington International Airport three hours early and accompanied him to the gate.

"I assumed Southwest would let him on early, before the herd of passengers gets on, because I'm not even sure he's tall enough to reach the overhead luggage," Cole said.

Cole said a succession of Southwest employees not only refused to let Danny board early, but wouldn't promise to help him meet up with his father.

A Southwest executive says the employees were just following company policy.

Southwest escorts children 5 through 11 who are traveling alone, but "once you hit 12, you're considered a youth and not an unaccompanied minor," said Teresa Laraba, the airline's vice president for ground operations.

Each year across the United States, hundreds of thousands of unaccompanied minors take to the skies. Airline officials say the holidays are second only to summer in numbers of solo children, a time of year that tests anxious parents and airline policies.

It's hard to know just how often things go wrong with unaccompanied minors. Airlines aren't required to report such incidents, although parents sometimes tell the federal Transportation Department. An agency spokesman said there were 36 complaints through last week, compared with 47 in the same period last year. The most complaints this year have been lodged against US Airways, 9; Delta Air Lines, 8; Northwest Airlines, 4; and American Airlines, 3.

In June, Northwest put two children on the wrong flights in Memphis. Both were reunited with family members — 12 hours late, in one case — and the airline said it was taking steps to avoid similar events.

Last December, a 9-year-old boy headed to Omaha, Neb., to see his father, who had just returned from a tour in Afghanistan, was stranded in the Denver airport by a snowstorm. The boy used a stranger's cell phone to call his family. His mother complained about the response from United Airlines after the flight was canceled.

Policies for unaccompanied minors vary throughout the airline industry.

Southwest doesn't charge extra for unaccompanied children, but most other U.S. airlines do. Some parents say they were surprised to get to the gate and then learn that their child's trip would cost an extra fee — up to $100 for domestic trips, more for international ones.

Airlines say they're doing all they reasonably can to safely accommodate more young travelers.

American Airlines, the nation's largest carrier, estimates that it carries more than 200,000 unaccompanied minors each year. While that's a tiny percentage of its 98 million boardings last year, the number is growing, according to spokesman Tim Smith.

"It's probably more a social phenomenon, with more single-parent families where the parents live in different cities, and more kids going to visit grandparents, and more kids going to summer activities," Smith said.

Julio Garcia, a real estate investor in San Diego, said his two sons were among eight kids from 11 to 16 years old who were nearly stranded 1,500 miles from home in August. They were flying home without their parents after spending three weeks at a French-immersion program in Paris.

The parents paid Continental Airlines extra to have the four youngest children watched, but not for the 15- and 16-year-olds.

Storms caused the plane to be diverted, and when it finally got to Houston, the children had missed their connecting flight to San Diego. Continental found seats on a later flight for the four youngest, but Garcia said an airline agent told him the other four — three boys and one girl — were going to a hotel.

"My eldest called and said, 'They just hauled the little kids away and left us standing here,' " Garcia said.

Garcia said he spoke with three different Continental employees, and told a supervisor, "Let me get this clear. It's Continental's policy to leave unattended minors stranded in an airport? How can you leave them in a hotel room? A hundred things can go wrong."

A Continental spokeswoman, Julie King, said because the parents didn't pay the unaccompanied-minor charge for the 15- and 16-year-olds, the airline had no idea they were traveling with the four younger children. The airline doesn't ask ages of other passengers, and it put the two groups of kids on different records, she said.

"We have strict procedures that apply to children traveling alone that ensure they have a smooth travel experience," King said.

Experts on family travel say there are common-sense rules that parents should follow when arranging solo trips for their kids.

Sarah Schlichter, editor of the Web site The Independent Traveler, said parents should pick nonstop flights in the morning so they can rebook if the flight is delayed or canceled.

Parents should give the child written instructions on what to do in case of flight delays or cancelations, including emergency phone numbers, and a calling card, Schlichter said. And have them carry a recent picture of the adult who will meet them at the other end, she added.

Natalie Windsor, author of "How to Fly for Kids," said parents should prepare the child for the flight, especially if it's his or her first solo trip. And, she said, create a rewarding reason for making the trip so it's fun instead of intimidating or dreary.

Danny Cole's story had a happy ending. Before leaving the Baltimore airport, an off-duty Southwest flight attendant getting on the same flight promised to stay with him until he met his father in Houston.

But Susan Cole said the episode left her angry and her son crying. She thinks 12 is too young for children to fly unescorted.

Laraba, the Southwest executive, said the airline has recently heard from other parents who share Cole's opinion. She said the airline is considering changing its policy.