UHUH!
Being a parent who often flies alone with 3 kids I am pretty organized, not to mention the briefings we always do to the kids before any departure...(briefing time...listen, be prepared and repeat!), but I have some simpathy for those parents... even if I don't think that "IT CAN HAPPEN TO ANYONE".
Just... Thanks god it was an AIRPORT, and not a mall, or a park, or a restaurant.... it can be dangerous everywhere for a kid, but may be, and this is the only consolation for those parents - an airport is a safe place...
Anyway I think that is not fault of the airline. not at all.
true is you parent, we parents, are the only responsible for our children.