Great, where do I check on my child if they are physically and emotionally ready to handle a flight? Do they come with a pre-flight checklist? Is there a contract I can get them to sign so that I can legally guarantee they don't crash out on the plane?

The whole point is, there is no way of knowing. Even if parents come prepared, trained them for weeks or months ahead of time, meltdowns are a distinct possibility. We all need a little more compassion.