Since I would definitely not live in this house if I didn't have the kids I used the cost of an apartment where I would likely choose ($350 mo less than my house payment). I used 10% of electricity and water for each child (which is probably not enough on electricity because I wouldn't be heating/cooling this big house) I also had to use a percentage on groceries and I again used 10% (which is probably not enough since 1 is a teenage boy).
The rest was actual cost. I didn't assign them any cost on things I would have with or without them (cable, internet, etc.)
I also didn't include incidentals like field trips, haircuts, increased gas for my car for being a taxi service, school projects, class ring, yearbooks, upkeep on this house, etc.
I'm NOT complaining about what it costs to raise my kids. I just did the spreadsheet in case their dad ever asked for an accounting. It's on my work computer and I don't remember exactly how much the difference was but I do know that the court estimate was too low.
And before you say anything about moving to a cheaper house, I would love to do that but this is the only home my kids have ever known and it was important to them to remain here for now, especially since my son is in the 11th grade. A 3BR appartment would run about the same in rent in this area so we would have to move to another county to see any difference in rent/mortgage, which would not be in his best interest to uproot him in the last two years of high school.