Having four kids with some in the teenage years, I can tell you costs are staggering. If you don't manage them, it can be staggering. Having one child probably would be the most costly as you have economies of scale with the others to a point, four puts into loss of scale.
Housing- How often do you hear that we need to move to xyz because of the schools. This means going from a 1,200 sqft house to a 2,800 sqft house in a higher cost area (for the schools)? The City I live in, that would be a $250,000 difference.
Health Care - As an owner, Self & Spouse cost of $1,121 per month vs. Family $1,506 = So one kid costs $385/month for medical and $59 for dental or $5,500 a year with copays, etc.
Schooling I have chosen to save and pay the tuition portion of each kid which is about $60k per kid, if you wanted to pay room and board at $40k for a $100k for public school for 4 years. So amortized over 18 years $3,333
Throughout the years there are camps, sports, music lessons, babysitters, etc. This is easily $1,500 per year.
Add clothes, food, vacations, and entertainment and you are at another $1,000 per year.
There are probably about a $500 a year per kid in various other school fees.
Food can be staggering if you go out for meals, but also a lot more. $1,500 a year?
Presents and other miscellaneous amounts add up to $667
For a total of $14,000 a year+ housing + car when they turn 16:) + $25,000 wedding:) + help with a downpayment, etc.
The biggest cost for many is the loss of income from a spouse and/or not going after full pay potential as it is hard to do with a kid. For two professionals, this could be $500,000+ over 18 years.
$14,000 x 18 = $252,000, then you add in the larger house in a better area, bigger car, loss of income potential and you are probably closing in on a million.
Of course, if you are mustachian you can mitigate all of these expenses and maintain full income earning throughout having kids. I think a lot of people are in shock if they add up the true costs of kids. I think many here will be shocked that they do cost more, maybe not the amounts that you hear in society, but still sizable.