In terms of student loans, the maintenance loans haven't gone up in line with rent, and they are means tested- in most families with 2 full time working parents, the loan a child gets won't cover their accommodation costs, let alone other living expenses. The current expectation is that parents contribute. In 15 years time, this may have changed again, though!
Yes, teenagers can get jobs, but most parents do help out in the uni years a bit, especially with e.g one off big expenses like deposits etc, which students often can't afford up front.
That said, I'm not sure it's as crippling as childcare is now!
I do think when you factor in childcare etc, this is probably the most expensive time, but equally during the teen years you may have to factor in higher housing costs (they literally take up more space, even if sharing a room), higher bills (using electronics + long showers + heating on in the day if they are at home and you're not etc), higher food bills- teen boys genuinely may need over 3000 calories a day, plus the things they want are more expensive- at e.g. 13/14, it's hard to say they need to pay a phone contract themselves, or similar. And that's without factoring in an expensive hobby!
I think after nursery, there is probably a dip in costs (although if you need wrap around childcare, maybe not as much as you would hope)- maybe around 10/11 or similar is a cheaper age, as less childcare may be needed, plus they may not have such expensive tastes yet. I think once they hit secondary school, costs can start to increase again, probably peaking around 16-19!
However, as others have said, you can at least have sensible conversations with teens about what is/isn't affordable, whereas childcare your options are very limited!