Derek Dombrowski, media relations manager for Spirit Airlines, said there is less urgency to get on board Spirit planes because the airline has assigned seating.

"We provide family boarding at the beginning of the boarding process and have no requirements on gender or number of adults."

Kirsten Wenker, senior communications manager with the Sun Country, said families with infants or small children are invited to board early together.

"We announce at the gate that any families with children in different boarding zones should all board together."