Inkbunny's position is that laws covering depictions of children or minors define them as persons under the age of X - and furthermore, that a "person" for the purpose of these laws is inevitably a human being, or (in some jurisdictions) very close to it. Thus, "cub porn" cannot be "child porn", as it does not involve a child, in the legal definition of the term.
This is particularly well-supported in the USA, which has gone to the trouble of defining "person" as a member "of the species homo sapiens":
In other countries, it is also commonly held that non-human animals do not have the same status as humans - hence, you can imprison them, eat them, etc. Having sex with them may be forbidden; but that's because a human is involved, or because it harms an actual animal. We do not forbid animals to have sex with other animals.
In accordance with this, Inkbunny does not permit submissions to depict human beings in sexual situations, or to show their genitals or arousal. This prohibition also renders bestiality laws inapplicable.
In the UK, the law covers material which appears to be of a person, even though one or more elements are not of a person. Parliamentary discussion of this indicated that it was focused on the addition of ears or antennae to otherwise human characters, and so our policy includes "neko" characters and others which are essentially human.
We do not forbid members from promoting such depictions for the benefit of those who wish to see them and feel they are legally safe to do so; but for the sake of those who don't, images on Inkbunny must not contain such depictions. Promotional submissions should have keywords applied permitting members to avoid them through our blocking system.
Fur Affinity's decision to forbid "cub" art was made on commercial grounds, not legal grounds:
They may now be using legal grounds to justify the removal of such images; if so, we believe they are mistaken.
On a related topic, Softpaw Magazine, which was dedicated for such material, was for several years openly printed in Canada and imported into the USA without issues:
Inkbunny's main server is currently located in the Netherlands. A summary of Dutch child pornography laws can be found here:
I am not aware of a definition of "person" in their criminal code, but their civil code includes the statement that "No servitude of persons, of whatever nature or however described, is tolerated":
It seems unlikely that zoos (of which there are many in the Netherlands) would be possible if this were held to apply to species other than humans.
As the Netherlands is in the European Union, the case law in Sweden may also be relevant, in which a man possessing non-realistic manga images was ultimately found not guilty of possessing child pornography:
Should the matter arise, we would vigorously defend our position, as we believe there is no public interest served in forbidding the depictions of fictional non-human characters in sexual situations.
We have never been contacted by any law enforcement on this topic - or any other. We suspect most prosecutors have their hands full dealing with images and instances of actual child abuse, which we do not host or support.