Sounds like excuses to me....
Again, crying is one thing, throwing oneself on the ground and having a temper tantrum is quite another... and notice that that surgery did not play any role on the flight they took a few days before.
Still sounds to me like excuses being made by parents who don't want to believe their child could do anything wrong and refuse to discipline them properly.
I can feel for any parent who's dealing with a child that is worked up and has no way to deal with it.. IE child is too small to communicate what is going on.. I've been there, I think just about anyone with a child has been there... but by 3 they are old enough to communicate issues, and throwing oneself on the floor screaming at the top of ones lungs is not acceptable behavior for a 3 year old.
This "its normal" is BS, its a result of poor parenting in all but children who have mental issues. Children behave how they are allowed to behave. Yes, strong willed children can be more of a handful than others, but even they will behave if handled properly.
All parents love their children, but only the dilluded ones believe their "precious little darlings" can never ever do anything wrong of their own accord.
Okay, I have tried to argue on behalf of parents with sick children but there is no winning. Okay, sick or not, kick them off of the plane, I give up.