DALLAS – American Airlines separated a 5-year-old girl from her mother and 7-year-old sister on a flight from Dallas/Fort Worth International Airport to Detroit last Saturday.

"It was awful," said Amy Buchler, 40. "I have a daughter who's already very sick and now I have to worry that she's sitting by herself, not knowing who's going to be sitting next to her."

She and her daughters were spending spring break visiting grandparents in North Texas last week when Naomi, age 5, got the flu.

"We were scheduled to fly back Wednesday night but we had to reschedule to Saturday," Buchler said.

When she booked online, the website stated she could purchase premium seats or it would assign regular seats at the airport.

Buchler did not purchase the premium seats, but instead waited to get to the airport where American would assign them in the main economy cabin.

Buchler discovered American split up her children’s seats, putting Naomi in row 17 and Amy and her other daughter in row 7.

Buchler said a ticket agent found Naomi a window seat in row 12, which would make it easier for her to find someone to switch.

"I felt like the airline wasn't willing to help at all," she said. "It was just me negotiating with other passengers to try to get us to sit together."

American said it's rare that families are unable to sit together. In fact, 72 hours before every departure, American said it runs a computer program trying to sit passengers next to their traveling companion.

But the Buchlers didn't book until the last minute and didn't discover until they got to the airport that there weren't three seats together.

Congress passed a law last year requiring airlines to seat children younger than 13 with their parents but it doesn't go into effect until July.

The Family Travel Association said this is another case showing why the legislation was overdue.

"It's really important for families, like anyone else traveling in a large group, to book as early in advance as possible,” said Rainer Jenss, Family Travel Association. "The advice is to check with your carrier or call a travel agent. To be honest the travel agents have relationships with airlines.”

Jenss said to call the airline directly to make sure there are seats together rather than booking the flight on the internet.

Still, it's not always possible to book in advance. Naomi got sick and her mother had to delay their flight home to Michigan.

"What if my child had allergies and they offered her candy that could have made her sick?” Buchler said.

Her father, Christophe, raised a different worry.

"What do you think is going to happen in an emergency?" he said. "Will she know what to do? Will the person next to her help her."

Passengers accommodated Naomi on this flight but airlines aren't required to do so until later this summer.