Southwest Airlines Community

It is not really "family boarding".  The process is like this:   When an individual under the age of seven (six and under) is on the flight, you can have UP TO TWO ADULTS board with that individual.   So, for family boarding to activate, you must have an individual under the age of seven.   Since you have two under the age of seven, up to two adults can board per individual under the age of seven. ... View more

See elijah's esponse to the question you asked.   https://www.southwestaircommunity.com/t5/Family-Travel/Checked-Car-Seat/m-p/93647#M1701   But to answer your question, boxes are acceptable "luggage."   You'd pay exra if the box is more than 62 inches (height+length+width) or it it weighs more than 50 pounds ... View more