Sigh. Really? Do we really have to go through this again?
First: There is no "Lost Gospel." The document in question has been well known to researchers for some time. The text relates to the story of Joseph (he of the not-so-technicolor coat) and Aseneth, a figure mentioned in Genesis 41:45 and who is the daughter of a Priest of On (Heliopolis) and bears him two sons, Ephraim and Manasseh. On the surface it is an explanation as to why Joseph could marry the daughter of a pagan priest and how she converts to the worship of the God of Abraham. Admittedly there is some strange stuff in it. She is locked in a tower where she has a vision of an angel who gives her a divine honeycomb to represent repentance. Bees surround her. Some die some go back to heaven. You can read the whole thing here. It does probably have some occult overtones (a Gnostic initiation ritual perhaps?) and the version we have might be a Christian work,due to the mark of the cross on the honeycomb, but perhaps of an older Jewish document. The original likely was in Greek, but we do not have it. We do have the work in other languages and in at least two different variations.
Second: Mary Magdalene, while a much storied figure, is not a particularly well documented one. There are a dozen passages that mention Mary by name in the New Testament, with most of those associated with her presence at the Crucifixion and later at the tomb. From Luke we are told that she had seven demons cast out of her and that she supported Jesus financially in his ministry. I by no means want to down play her significance. She is mentioned by name more often than almost all of the apostles. Yet most of what people think about her is the creation of later generations. It is not until 591 that Pop Gregory associates her with the prostitute who washed Jesus feet and also Mary of Bethany, sister of Lazarus. Its the books that the early church rejected, not 'lost' - if you throw something away you know exactly where it is, that give her a place of preeminence among the apostles as the favorite student of the Gnostic Jesus. In particular the Gospel of Phillip describes Mary's relationship to Jesus as koinōnos, a physical and spiritual pairing of man and woman. Thus the tradition that Jesus and Mary were married. Mary is also credited, by the way, with Easter Eggs and she even shows up in the sacred writings of the Baha'i.
So, we have a work of admittedly questionable providence and likely occult symbolism. However, there is no clear historical or literary connection to even those traditions that tie Jesus and Mary together sexually. Its simply a sensational headline for the news to grab and generate interest in a book by man known for questionable scholarship.
One more thing to think about: If Jesus had children roughly one thousand nine hundred and eighty four years ago in Palestine, and if we assume just two children per couple living to reproductive age, pretty much all modern humans would be descendants of Jesus.