I think that it is actually unsafe for small children to sit away from their parents.
Just think about it: who is going to check that they are safely strapped in?
If a catastrophe happens, what if nobody is willing to help them get out of the aircraft? A parent is usually willing to die to save their own child but may not be as keen to put themselves at risk for someone else's
There are good reasons why a parent needs to sit with their own children when they are under a certain age - say 10/12. I think that is a health and safety issue and that making them pay (in other words putting a tax/premium on travelling with small children) is just wrong. (But then, so is charging people for wheelchairs and they have done that.
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When my kids were small I would have just refused to sit down if I had not been able to sit with them (or at least have one with me and one with their dad). When I was cabin crew, I always managed to sort it out for people - it is really important!!!!!
