The earliest evidenced appearance of the word "cambion" in the sense of an offspring of two demons is in the 1818 French-Language Dictionnaire Infernal. The 1825 edition of that book has the following entry: CAMBION, -- Children of Demons. Delancre and Bodin believe that incubus demons can unite with succubus demons...
In the Encyclopedia of Occultism and Parapsychology the cambions are again said to be the direct offspring of the incubus and the succubus, foregoing any need for human involvement.