Probably some form of kids media that included people being eaten. I'm convinced most fetishism stems from a kid trying to make sense of something they witnessed which they found weird and fascinating, later crossing their wires during puberty and resulting in a weird kink they can never fully explain aside from that early fascination. Lola Bunny creates furries, tickle torture creates feet people, that Willy Wonka scene creates inflationists.
Is there any kids media portraying eating people that would have been popular around the time that many current vore people were kids?
This is absolutely the cause. Fetishes (in the absence of DeviantArt grooming) are born of scary/confusing imagery being presented to a young, young child, and I have yet to see a better explanation. Abusive and neglectful parenting exacerbates this phenomena.
I can give you two examples of films that anecdotally caused this fetish: Jurassic Park and Shrek.
I knew a guy who was normal. Successful. Not autistic. Genial and sociable. A believer in God. Since meeting him, I've paid more attention to the origins of these fetishes. No one's bothered to seriously study them and most of the outspoken fetishists are so retarded they can't even comprehend that it's abnormal.
He confided in me that he had a strong vore fetish since he was FOUR years old, and it was triggered specifically by Jurassic Park. The T-Rex swallowing someone alive broke his little brain irreparably. Later on, he was aroused Farquaad's death in Shrek and would rewind the VHS there over and over.
I learned from him that vore is spectrum and there're hundreds of genres you can't even wrap your head around. He hated inflation, he just liked the idea of being swallowed and digested. He told me there's shit like soul vore, sentient fat, and being consumed by pretty much any body part.
All of this sounds extremely demented (and it is) but it sounds like it was completely out of his control. He didn't have attentive parents to comfort or explain shocking things to him. Apparently, he was exposed to all sorts of R-rated horror films as a little kid because that's all his mother liked to watch. Is it any surprise that it messed him up? Every kid's different. You risk traumatizing them or burdening them with an embarrassing life-long kink if you don't care about what they watch.