The creators of Ninjago, Dan and Kevin Hageman, posted this to someone who put this on Google and I found it so here it is.
Reasons to think of this...
1. Jay doesn't look a lot like Ed and Edna.
2. He doesn't even sound like them.
Also, I am not sure how Jay got the scar on his eyebrow. Perhaps to be marked and able to find him again? I mean, maybe they had to send him away or something. Then Ed and Edna found him and raised him as their own. They never told him, then joined ninja.
That's just what I think. But comment below on your opinion.
