I agree with bellatrix. Many of the 'expenses' associated with children are choices made by the parents
I do wonder if people making these comments have ever had kids. Certainly Bellatrix - on her food thread that I read just before this one - talks about feeding her and DH - '2 people' according to her thread title. Maybe she has DC that have grown and left home, or maybe she has no experience of the costs of raising DC?
I have DC of 17 and 20 - never had designer clothes, nor expensive phones (basic Samsungs at £10/mth until iPhones in last year or 2 as xmas presents, on £7.5 sim only contracts), no expensive hobbies (but still done athletics, football, Guides, Scouts - which needed subs, sports gear, petrol for lifts etc).
Kids of all ages cost money, but teenagers are effectively adults in terms of food (both mine love food and have great appetites), clothing - they grow so much at this age, heating/showers/baths (not exactly a parental choice), electricity (running laptops for school work, charging devices etc), extra washing - again not a choice.
School uniform - our high school completely changed the uniform a year after youngest started, so all the money we spent kitting her out for first year had to be spent again. DS had to have some new uniform that he was only going to use in his last year.
Eating out in any form - even just a coffee/cake or lunch, costs 4* as much with teenagers (who are much more likely to want a cake or other snack with their coffee than an adult). My 17yo DD can eat for England, she is always hungry. I don't begrudge her, she was a small prem baby with a heart defect, needing supplements to build her up when a baby, but it certainly ups the cost of all of us going out. Yes I accept that eating out is a choice, but how many families never eat out at all?
So yes parents can, and some do, choose to splurge money on kids, but I would say most of the costs of teenagers are definitely unavaoidable needs rather than wants.