If Jesus had a son or daughter with Mary Magdalene, what would I expect? That there would be a legend or a story of a miraculous child in a land accessible from Judaea starting in the first century CE.
Jesus’ seed, spermos in Greek, is Gematria 277

You’ll notice, “ferry boat, scattered, family, race, strength.”
Remnants of the seed fighting the dragon is mentioned in Rev 12:17. Remnant is Cheser – 808 in Hebrew

808 + 277 = 1085, which is “wreathed work.”
So I take from that, that I’d be looking for a legendary mother-son or mother-daughter with supernatural abilities and divine connections. They should be symbolized by a wreath, like you’d hang on a door.

Celtic tradition honors Mabon and Madron; Mabon was hidden to be raised in secret. Makes you think, right?