There is not a toggle in ESO for disabling or enabling gore.
Aww bummer. Im trying to find RPGs my little sister and I can play together. Ill keep looking. So far we got WoW, but she likes the go anywhere, do what I want, type of game so WoW doesn't cut it. This game would have fit perfectly too, but I think the gore would ruin her innocence. too real.
If there is an addon for this out there, I cant seem to find it either.
Not really a viable way for an add-on to remove blood effects ad they are tied to abilities and if the API allowed for abilities visuals to be changed you would have a lot of lets say "interesting" videos on youtube.
Tl;dr really weigh the fun you have in game vs the business practices you are supporting.