I'm afraid I have to side with the government on this one. Imagine how many more kidnappings would take place if you could claim someone else's child as a dependent. All you have to do is make sure they get enough of the scraps you throw down in the cellar before the rats get to them first, and change their water dish often enough that they don't get diptheria before half of the tax season is through.
Most of the kidnapped children have been kidnapped by one of their parents (i.e. divorced parents had shared custody and mom or pop decided to take the kid with them abroad without the consent of the ex-spouse). And there's got to be easier ways to make money than to keep a feral child in your basement so you can get a few grand deduction at the end of the year.
... unless you are running a sweatshop, maybe.
Listen to me, baby, you got to understand, you're old enough to learn the makings of a man.