In the Japanese films, Sadako was an adult already when she fell down the well and survived 30 years in it. So she's at least in her forties, according to Wikipedia. In the American version I think they changed her to a child but also changed her name
Boy.... Uh you really haven't paid attention to Disneys animations for the past several decades have you...? Since the source material featured incredibly underaged characters for some stories, Disneys version made them adults. So are they "bad" and still children as well...?
Look ....I definitely do not defend when they have viably looking minors in anime and try to say "oh they're actually a dragon" or "they're 1,000 years old" but this argument for this situation is kinda moot if the depiction is clearly not of a 12 year old