The fact that parents "should" know better doesn't excuse the airline from taking care of one of its customers stranded in an unfamiliar place, whether that person happens to be 15 or 50.
To suggest that parents should sit at home refreshing AC.com every 5 minutes to monitor for missed connections, with a spreadsheet of alternate routings whenever they have a kid travelling... c'mon. The mom lives in Geraldton. She may never have been on a plane in her life. Not everyone on earth is an FF or even an occasional traveler. Yet these people and their families from time to time need to travel for major events like medical treatment, education, weddings, funerals, or sure, going to visit Dad in Denver.
Rather than expecting all 7 billion people on the planet to know the intricacies of airline travel, I expect the employees of airlines to be available and willing to assist when a passenger encounters trouble at said airline's flagship hub airport. That's basic customer service.
When the passenger is a minor who can't get in touch with his mom because she's driving from her home in Northern Ontario to pick up him, it becomes a matter of basic decency.