@RealDeal:

Just my opinion, as someone who plows through the galleries at Renderotica on a regular basis as a part of his duties...

It's pretty simple: If it looks like a kid, don't do it. If it looks old enough to easily pass as 18, go for it. The FAQ @ R'otica is simple and straightforward about such things (I'd link to it, but given the Prude Patrol's pusillanimous proclivities pertaining to piles of porn, it's prolly better if I just reposted it verbatim):

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First up, we do NOT tolerate anyone pushing paedophilia. We simply have no tolerance for depictions that can appear to be that of children in a sexual situation. Yes, we know that the US Supreme Court has ruled somewhat recently about 3D/CG depictions of even outright child porn, and that the ruling says that at this time it is not really actionable under the law. We simply don't care - we won't allow it. We're pricks like that. When it comes to Lolitas, Poppets, and anything pre-pubescent? We don't want it, we don't appreciate it, and we will delete any instance that we find of it. Don't like it? Go open your own website that specializes in such subject matters, and you deal with the fallout.

Subjective as Hell, ain't it? But - it is simple. If it looks like a kid, it doesn't stay. Don't like it? Go open your own website and post 'em all you want there. The only real differentiator is, we actually use our heads and don't over-react.

...and that leaves us to your situation - just use your head. If the characters look like kids, either grow 'em into adults or don't do it. Nobody is twisting your arm to make the animation.

/P