Generally speaking I would say never. There are exceptions to every rule, but you would need to describe the reasons why you think there should be an exception.
Children should not be involved with the legal fights and financial arrangements of divorce. At age 6, 10, 14, they certainly shouldn't be put in the middle where they would feel that conflict between the parents is or was their fault. There is nothing to gain by bringing them into this.
During the mid-teens I would say that if a couple has been separated/divorced for years and the situation has settled out it might be less of an issue, but I would still say there would have to be a compelling reason why.
Now often parents can have serious budget restrictions and teens want clothes and cars and trips and nights out. Parents certainly need to sit down and go over some basic financials with their kids, but I don't see any reason why anyone would need to bring the legal documents spelling out support payments into it unless it was to complain about the other parent somehow.
If the child were sitting at a table with both parents, the parents were by that time amicable, and there was a positive intent to explain the full financial process of the family budget so the child could learn from this to plan their own life and there was no intent to blame one side or the other, then I could see some reason for it, if the child was genuinely interested. But looking back at me and my friends when we were 15 or 16, I have a hard time imagining it.
Even at later ages, when the children are in university, left home, etc, what is the motive? To finally satisfy the child's curiosity? Or to raise bitterness against one parent? I can't think of a good reason to want to. That reason may exist and I would be happy to read other comments and experiences but I don't see it myself.