The airlines that do - and don't - guarantee families will be kept together.
ADVERTISEMENTSome have called it the parenting tax: when caregivers are forced to pay for the privilege of sitting next to their children on a flight.
But the charge may soon be banned.
The US Department of Transportation is proposing a new rule which would mean American and foreign airlines have to seat children aged 13 or younger next to their parent or caregiver for free.
“Flying with children is already complicated enough without having to worry about that,” U.S. Transportation Secretary Pete Buttigieg said.
The Biden administration estimates the rule could save a family of four as much as $200 (€185) in seat fees for a round trip.
Buttigieg pointed out that four airlines – Alaska, American, Frontier and JetBlue – already guarantee that children 13 and under can sit next to an accompanying adult for free.
But what about European airlines? Since many travellers choose to fly with budget airlines to save money, are extra fees making their flights not so budget?
Here are the rules for some of Europe's biggest budget airlines.
Will easyJet seat families together for free?
If you want to absolutely guarantee to be seated next to your kids, you'll have to pay for the seats on easyJet.
They say: "We’ll make sure each child under 12 is seated close to an adult on your booking. However we may only be able to arrange this at the airport or on board, which can cause delays for you and other passengers, and not everyone may be seated together."
The budget airline says that seats are allocated on a first come first served basis, so the earlier you check in the more likely you are to be seated together.
Jet2: One of the best budget airlines for families
British budget carrier and holiday company Jet2 is one of the most accommodating to families with kids.
They say: "We will always endeavour to seat children and infants under the age of 12 next to their accompanying adults. If this is not possible for any reason, we will ensure children are seated as close as possible, and no more than one row away."
Ryanair: The adult must pay to reserve a seat
If you're flying with Ryanair, at least one adult will need to pay to reserve a seat. Then up to four children can sit with their parent.
Note that adults who don't buy seats together are likely to be split up on Ryanair.
ADVERTISEMENTVueling: No guarantee you'll be sat with your kids
The Spanish airline owned by Iberia says they can't guarantee you'll be sat with your kids.
Specifically, they say: "The system will always try to keep passengers in the same booking together, but this is not always possible due the number of seats occupied on the plane."
The best bet is to select seats together online - some will be free, some paid for. Or check-in online as early as possible, it opens seven days before the flight.
Vueling says that if you check-in at the airport, "we'll try to allocate you a seat next to your child, though this is subject to availability so we cannot guarantee it."
ADVERTISEMENTWizz Air: Pay for seat to make sure you can sit with your kids
Make sure to pay for your seats on Wizz if you don't want to be split up.
Wizz says that it will seat children with an adult without them having to pay. But if the adult hasn't paid for a seat, there's a chance the family will not be seated together.
