I know of green card cases where it's (1) bring in wife from foreign country (2) she also has 3 kids over there that need to get cleared for the kiddos to come to the US and live here - all legal and above board, nothing undocumented.
In order to keep it legal and above board, the US state assumes they are not her kids until proven otherwise. So yes, a DNA test is required. The other stipulation is a state department person needs to be in the room with the kids blood is drawn. A lot of red tape!
On the one hand the whole thing seems aggressive and strict. On the other - you can imagine that these rules went in place from bad experiences i.e. the DNA test existed because people were scamming the "bring children over", and then a state department person needed to be present because people were scamming the blood draw. It's another example of a few bad apples ruining it for everyone.
