I think a lot of it depends on how you parent - and where you live, too....so take that into consideration when looking at my prices, but...just as some of the prices that I can list off the top of my head...
I have 2 children. One is almost 3, and one is 6.
For my 2 year old, we spend about $50/monthly, for diapers. Or $600/year. Hopefully we'll start potty training this month though, so that cost may soon evaporate. But that's a starting cost for you to base it off of.
Day care - we pay $150/wk for four days. That is $7,200 a year. BUT...we also have a 6 year old...and she has to go into a Summer program when school is out. It's $110/wk for her, and it's a 10 week program - so that's an extra $1,100. So that's $8,300 for the year in daycare. But also, during the school year - the 6 year old attends morning (and only the occasional afternoon) latchkey. That is about $15/wk for the remaining 42 weeks of the year, which is $630. So the total so far for daycare is just under $9,000 for a year. We'll call it $9,000, because during the year we also have to pay deposits on the day care services we use, and pay occasional babysitters so we can go out, etc.
As far as insurance, I'm not exactly sure ... but I know that my husband pays about $70/wk for insurance (health, dental, vision, prescription) for the three of them. I have my own. So that's about $3,640 a year. That's not including copays, or anything else that insurance does NOT cover. Doctors/hospital stays, prescriptions, etc... So I'd say about $5,000 a year for medical stuff.
We try to keep our monthly grocery bill to about $500 for our family of four. But that's really pushing it. It's probably closer to $600-700. So we'll say $600 just to put it in the middle. So that's $7,200-ish a year.
So far we're at about $21,800 a year.
Something else you also have to take into consideration as a "Cost" is missed work. When your kids are sick, you have to take off work. Just this month, because my youngest was in and out of the doctors/hospital - I missed out on over $500 worth of pay because I had to stay home with her. Obviously you have to hope that isn't happening ALL the time - but it's probably safe to say I miss about $1,000 a year staying home with sick kids.
Add into that clothes, birthday and holiday (if you celebrate) presents...and a lot of other stuff I skimmed over or missed completely because I'm not thinking about it..
Over $25,000 a year.
You just have to take into consideration that everyone's situations are different. Some people are thriftier, and can spend a lot less on food, clothes, etc... Some do cloth diapering, some make their own baby food...some stay at home so they don't HAVE daycare/missed work costs. It's really all situation-dependent...but at least now you have one person's breakdown to look at for comparison.