Are Classical and Renaissance statues and paintings of nude children CP?

I know this sounds like an obvious "no," but there isn't a simple, non-arbitrary criteria for differentiating between loli/shota hentai and legitimate art, for the same reason that there's no simple and non-arbitrary criteria for differentiating between art and porn.

Yes, you can certainly describe what you regard as the relevant differences between porn and art, but there's never gonna be anything even approaching objectivity in that discourse, and policy-making is something you have to be a total autist about or else nefarious actors will take advantage of ambiguity to abuse the rules to their advantage.