I think it's silly to distinguish between loli and 3D children, and I don't see any meaningful difference between the two. Let me explain my thought process:
We make sense out of the things we see by identifying patterns and attributing them to general forms. In more straight-forward language, we are able to identify objects because we have seen an object similar to it in the past and can either infer what it is by comparison or directly identify it because it is the same type of object as one we have seen prior. This is why you can tell that something is a hat, for example, even if the design of the hat is something you've never seen before. This is also how we identify what things are in art, because we can see the patterns that create a recognizable form. Take pic related, for example. You can recognize that the object on the table is a melting clock. But have you ever seen a melting clock before? Probably not, but you know what melting looks like, and you know what a clock looks like, so you can figure out what you are looking at by identifying the patterns in common with other objects.
So how does this apply to loli and 3D children? Well, loli is a bit of a nebulous term but it can be generally understood to mean childlike in appearance (and possibly also behavior). So when you look at a picture of a loli what forms, what things in your mind, allow you to make sense of this collection of lines and colors? Most people would answer that they recognize it through comparing it with a child. This is further the case when you consider that young children are often the models for loli. Even in non-pornographic contexts, a famous example is yotsuba, who is modeled after various children. So really when you are looking at loli art, you are looking at an image of a child, and so it would follow that when you feel aroused at loli art, you are feeling aroused at an image of a child. Feeling arousal from children is pedophilia.
If there is a flaw somewhere, I'd love for someone to point it out to me, but ultimately I think it's just a matter of forms.