Oh wow! That's maths beyond me! I'll give it a go from my perspective with a just turned one year old...
Say £40ish a month in nappies
Say around £10 on wipes
Say £10 on nappy cream
Say £100 a month on food (for the baby - ingredients, snacks etc)
Mine is just coming off formula but could go through a box of formula a week (£11 a box, for today's calculation let's say two a month so £22)
For arguments sake, let's say clothes even out at about £40 a month (for everything from coats to socks, a couple of outfits a day for when clothes get wet, etc at nursery)
Childcare for mine is £75 a day and she is there 4 days a week (I work full time and have very little in the way of family to help out) so for me that's £1200 a month.
So a total of £1382 divided by two is £691.
Again, I am sure it could be done a lot cheaper (re clothes and stuff, I've just thought about what I've had to buy this past month or so for the colder weather and going up a size, and I buy Tesco clothes!) and as you can see, for me it is childcare that is the killer, but I had no choice but to go back to work full time, and as I say, no family really to help out more than one day a week. Plus big expenditures for example, I've just had to buy the next stage car seat, that's another £140, but supposedly will last til 12...
And that doesn't include petrol, car maintenance, house bills (gas, electricity, internet, water, council tax, etc). Again, I know that there are so many ways of cutting corners and reducing the amount, but it is a substantial amount of money that needs to be spent simply housing a baby each month if everything is taken into consideration.