For families with young children that have decided to fly for the holidays, the biggest challenge might not be packing gifts, finding COVID-19-safe airport transportation or herding the whole clan to the gate.

Rather, it could be coming up with ways to make sure fidgety toddlers wear their face masks in the terminal and during the flight.

As the coronavirus pandemic complicates family travel, parents are confronted with challenges they never could have expected to encounter. One is the widespread rule among airlines that even young children are required to keep masks on during flights.

Air carriers received more support for their rules when the Centers for Disease Control and Prevention offered “interim guidance” last month that echoed the policies of most airlines in saying masks must be worn by all passengers except those under age 2.

When it comes to packing up the kids for a year-end trip, how much trouble could parents expect to encounter when it comes to the mask rule? It depends, says Charles Leocha, president of Travelers United, a consumer advocacy group,  because airlines may be inconsistent concerning how they enforce masks rules when it comes to kids.

The level of enforcement may vary “from airplane to airplane, crew to crew,” given that some airlines give their flight attendants more leeway than others, Leocha said, even if they take a hard line with their written policies, which generally offer few exceptions, even for medical conditions.

There is little variation between carriers when it comes to the written policies. But one exception is Delta Air Lines, with a policy that states “young children who cannot maintain a face covering are exempt from the mask requirement.” It does not define “young.” Delta is also an outlier when it comes to letting people fly without a mask because of medical conditions, but it says those who do need to complete a “clearance to fly” protocol before they are granted an exemption.

Passengers who won’t comply with mask requirements on planes are often put on carriers’ no-fly lists, banned from future flights.

A Texas woman, Alyssa Sadler, had to leave a Southwest Airlines jet in August after her 3-year-old son, who has autism, wouldn’t wear his mask, the Associated Press reported. JetBlue Airways ejected Chaya Bruck and her six children when her 2-year-old daughter wouldn’t keep on a mask.

It’s not just happening in the U.S. but in Canada, as well: Aaron Munn was booted from a WestJet flight when his 2-year-old son spurned a mask.

“It’s foolishness,”  Munn told the CBC/Radio Canada.

Jodi Degyansky encountered the issue firsthand on a flight from Fort Myers, Florida, home to Chicago last month when a flight attendant raised objections to her 2-year-old son having pulled his mask down to eat. The aircraft was still on the ground, and Degyansky had hoped a quick snack would lull her son asleep, making it easy to keep his mask on him during the flight.

“I knew the mask would be challenging,” Degyansky said. All went according to plan: She got his mask on and signaled a thumbs-up to a flight attendant, who acknowledged it.

Too late.

By then, the pilot was taxiing back to the gate, where the pair were escorted off the plane, forcing her to buy tickets to fly home on another airline. Degyansky said they were observing Southwest’s rules; passengers are allowed to pull down their masks while eating or drinking. She also said she has no issue with the age limitation when it comes to masks.

“I am not a mom coming at this saying, ‘It should be 3 and up.’ We were abiding by what we were told to do. I am willing to do whatever it takes. We are not anti-mask people at all,” Degyansky said.

Since that ordeal, she said she has taken her son on other American Airlines flights without encountering any trouble.

Asked about her  situation, Southwest Airlines wouldn’t comment on any individual customer and referred USA TODAY to its face mask rule. According to that, passengers can take masks off to eat, drink or take medicine, but maskless moments must be “very brief.”

Rachel Starr Davis was ordered off an American Airlines flight in Charlotte, North Carolina, as she made her way home to Portsmouth, New Hampshire, because her 2-year-old wouldn’t wear a mask.  She and her child were moved to a later flight in which she said a pilot apologized and explained he understood the difficulties of traveling with a young child.

An American spokeswoman said that the airline’s mask policies have widespread acceptance among customers.

“The overwhelming majority of our customers support and follow our face-covering policy,” said American Airlines spokeswoman Martha Thomas in an email.