It depends on the expectations, though, doesn't it? It's only a luxury to have children if you put them last on the list behind your lifestyle - ie, can we keep up this lifestyle and still have children?
My GPs had 5 children. Grandad worked in the steelworks and Grandma was a SAHM. They rented a terraced house and had:
No central heating, no double glazing, no washing machine, no fridge, an outside toilet. No tv, no car, no foreign holidays. The DC had one Sunday best outfit and one everyday outfit. No phone in the home. She cooked exactly 7 meals - they had the same thing every week. Sunday was a joint of beef, Monday cold meat and chips, Tuesday she made a hash with the remains of the meat and potato and veg out of the garden, etc. My dad remembers that he had an old army surplus greatcoat on his bed as a cover - and he shared a bed top/tailing with his brother, til his brother left home to do National Service when Dad was about 9.
I'm not suggesting anyone is unreasonable for not wanting to live like this nowadays - but that's the lifestyle that one wage provided in the 1950s.
For myself, growing up in the 1970s and 80s we had no phone at home, no foreign holidays, only got central heating when I was at secondary school. My DP did not own a VHS player until after I'd left home and I remember ONE girl in the 6th form whose parents got a Betamax player and we all were so excited about watching films at her house when they were out. I had very few clothes and remember saving up my 60p an hour wages aged 14 to buy a £10 skirt in Dorothy Perkins. A chinese takeaway was for birthdays only, not weekly. I didn't eat Indian food until I was in my 20s and there weren't any restaurants around us. I push biked everywhere, and didn't do any activities out of school other than Brownies, and later joined the local hockey club. My DF had a professional job and we would have been considered 'middle class' rather than poor. We holidayed once a year on the continent by house swapping with another family for a fortnight, but most of my friends did not go abroad til they'd left home. My parents did not have a new kitchen, or buy new carpets or new furniture. They made do with the old stuff they bought.
All of the new technology, all of the new expectations of how people should live comes from perhaps the last 20 years or so. So, no, you can't afford everything. If you want your home to look Instagram ready, to have multiple foreign holidays, to run two cars, to have the latest phone, Sky, and your DC to have exciting activities after school every night then yes, this is for the rich.