Well, I have a nearly 3 year old DD and a 3mo DD. We live in a suburb near Newcastle.
OK, so I suppose if we didn't have the kids we might have rented somewhere smaller, but then we would probably have chosen to live in the city centre. Lets say we still wanted to live round here though, in a flat (as I don't think you can get one bed houses round here) so lets say there is an extra £100 a month on the rent and £25 on the council tax. Our utilities are about £70 a month, so lets say £30 of that is for the extra laundry and heating a slightly larger house. But you said to ignore bills, so I will.
Food is hardly anything extra, but I do probably get some things in that I wouldn't without kids. Being a SAHM means I have time to cook that I wouldn't if I was working, so I'd say that evens it out.
Clothes are mainly hand-me-downs, but if we had to buy them, I'd say maybe £30 - £40 for each size (so every three months) for the baby, the toddler is a bit more expensive as she wears more complex outfits, so maybe £80-£100 per size for her, but as she grows more slowly, that is only a yearly expense.
Nappies - the washables were mainly paid for with a grant from the council of £30, but we have topped that up with more expensive all in ones and so on at a cost of maybe £50. They have done both children though. Disposables are about £5 a week per child. Other toiletries (wipes, cream, nappy liners, bubble bath, shampoo, talc, lotion) might come to £10 a month.
No transport costs, as I would have a bus pass anyway if I was working and the kids go free.
No nursery costs, I'm a SAHM with good babysitters, but I think it costs about £15 a half day. You can get grants for 80% of the cost if you both work though.
Activities - dancing lesson costs £3.50, one playgroup we go to is £2.50, the rest are surestart so free. At home, we do crafts, maybe spending £2.50 a week on materials and play with toys, she has far too many, but I'd say we have spent maybe £100 - £200 on toys since the first one was born, and obviously they get recycled through children. The other stuff we do is free.
I'd say my main child related expense is drinks in cafes to calm down the toddler and so I can feed the baby. We can easily spend £10 in a cafe, just if we get a drink and a small cake each.
:/ I must have missed something out...
Anyway, we get about £120 a week in child tax credits and child benefit, so I think we are in profit by that reckoning atm...although I think costs will go up once the kids are too old for surestart and start wanting "things" and eating more food.