Like something out of a bad novel...

From the Telegraph:

The children share their birthday, are in the same class and their nicknames mean the same thing. But it was only when their parents started working together that suspicions were raised.
Now DNA tests have revealed that two 10-year-olds in southern Thailand were swapped at birth - even though one is a boy and the other a girl.
Both mothers had fainted when their babies were born and no other family members were in the delivery rooms, so there were no announcements of "It's a boy" or "It's a girl."
Questions began to be asked a decade later when the parents who raised Jirivuth Boonyu, the boy, came to work at the rubber plantation where those of Orawan Chanthont, the girl, are in charge.
Colleagues remarked on resemblances between each 10-year-old and the younger child in the other family - both sets of parents had a further child. A visual comparison followed and that invited further investigation. Thailand's central institute of forensic science settled the issue.

Very difficult for all concerned...