This is a bit like the "cost to keep someone in prison" figures.
You can get widely varying figures depending on what you include and what you exclude.
For example you look at the social workers and divide by the children
Well social workers have to be paid so why not add in the council administrative costs proportionally ?
There may be buildings so we add in the maintenance costs of those.
If you've a mind you can find all sorts of things to add in.
Chances are this probably came out of some sort of Freedom of information request.
If you want a scandle look at that
Freedom Of Information requests are mostly used by journalists - there were 121,000 of them in 2005 alone
The average cost to respond to each is about £300 and the cost is £10
That cost Local and National Governments £35 million