The latest video of a clash between airline passengers and crew on a Delta Air Lines flight focused the spotlight on confusing federal and airline rules governing travel for small children.

Brian and Brittany Schear of Huntington Beach, Calif., told KABC-TV that they were returning from Maui with their two toddlers when the dispute arose on April 23. They wanted to put a 2-year-old child in a seat they had bought for their 18-year-old son, Mason, who had flown home on an earlier flight.

Here's what contributed to most recent encounter on a flight to go viral.