Sorry but having the risk of anyone "having a meltdown and start scratching" could be an issue for other passengers or the crew. People buy a ticket to get from A to B, not to potentially get stretched by someone out of control. I sympathise with the parents but the crew absolutely did the right thing. Just like the little old lady who got violent a few months back on the TATL causing a diversion. Regardless of age people can still inflict harm on other and an aircraft cabin is no place for someone who is potentially out of control.
I'm not sure what the parents were trying to achieve but it hasn't worked for them and has backfired on them. Like I mentioned the catering situation is explained before boarding.