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, making it 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 to 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 was just back 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 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 Inc. 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 to 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 commonsense rules that parents should follow when arranging solo trips for their kids.

Sarah Schlichter, editor of 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.

“They should be flying TO something,” Windsor said, “not just going from mommy to daddy.”

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, even if she has to pay extra for the service.

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.

Here are highlights for the largest carriers. See airline Web sites for details:

• American Airlines: Fee of $75 each way for domestic and international flights. Ages 5 to 14, and parents may opt to pay for those 15 to 17 to travel as unaccompanied minors. Ages 5 to 7 can only take nonstop or direct flights — those not requiring a change of planes. Ages 8 to 14 can’t connect from another airline. Flights must be booked through a reservations agent, not the airline’s Web site.

• Continental Airlines: $50 each way for nonstop flights and $95 with a connection within the United States, Canada and Mexico; $70 and $95 for other international trips. Ages 5 to 14, optional for those 15 to 17. Ages 5 to 7 allowed only on nonstop or direct flights. No departures after 9 p.m. except on international, Hawaii or Alaska flights or trips of two hours or less. Not allowed on last connecting flight of the day to their final destination.

• Delta Air Lines: $50 each way for nonstop and direct flights, $100 with connections. Ages 5 to 14, optional for those 15 to 17. Ages 5 to 7 allowed only on nonstop or direct flights. Can’t be booked on last connecting flight of the evening.

• Northwest Airlines: $50 each way for nonstop flights and $75 with a connection within the United States, Canada, Mexico, Puerto Rico and the Caribbean; $60 and $90 for international trips. Ages 5 to 14, optional for those 15 to 17. Ages 5 to 7 allowed only on nonstop or direct flights. No departures after 9 p.m. except on international, Hawaii or Alaska flights or those two hours or less. Can’t be booked on last connecting flight of the evening.

• Southwest Airlines: No fee. Ages 5 to 11 and only on nonstop or direct flights not requiring a change in aircraft or flight number.

• United Airlines: $99 each way. Ages 5 to 11, optional for those 12 to 17. Ages 5 to 7 allowed only on nonstop or direct flights. Can’t be booked on last direct or connecting flight of the day except for connecting to and from international flights.

• US Airways: $50 each way. Ages 5 to 14 allowed only on nonstop flights, optional for those 15 to 17.

• Airlines policies on unaccompanied minors on their planes

  Major U.S. airlines don’t let children under 5 years old fly alone, and they require an extra fee for unaccompanied children from 5 to 11 — or 14, depending on the airline.

  Airlines reserve the right to demand proof of age, so have the child’s birth certificate or passport.

  Get to the gate at least 30 to 45 minutes early to fill out forms, and the parent should stay in the gate area until the plane leaves. Adults meeting an unaccompanied minor at the arrival gate must first obtain a pass from a ticketing agent allowing them beyond the security checkpoint.

  Airlines will not administer medicine to children, so if your child needs medicine that he can’t administer himself, talk to your doctor before booking.

Source: Airline Web sites and spokespeople