I prefer mature full-figured women and BBWs but censorship sucks so here's my advice:

Add fairy wings or something else that would make the characters "non-human" and thus not subject to the laws. Fantasy creatures are not governed by child pornography laws. If they're not human, it cannot be classified as child pornography because they don't exist in reality. Centaurs, fairies, nymphs, etc. will be ignored by the authorities and if anyone tries to give you any trouble you have a strong argument in your favor. It's doubtful that anyone would try to censor images featuring fantasy creatures.

The other option is to give them certain traits that would suggest that they're over 18 without changing their overall appearance. Piercings in strategic locations, smoking cigarettes/cigars or other activities that children don't/can't do. Appearance or portrayal alone isn't good enough for the authorities to prosecute. If it were, producers of pornography featuring actresses like Little Lupe or Sugar Baby would have been prosecuted long ago.

And include a disclaimer about the age of those being portrayed, to the effect of something like this (taken from an adult DVD site):

"The use of word teens, teen or young on this website refers to models who are over the age of 18 years old. The manufactures who have porn DVDs for sale on this website, state directly on their products, that all actors/models depicted in their porn videos are over the age of 18 and that a record of proof is on file. We carry porn movies directly from the manufacture. The records required by Section 2257 of Title 18 of the United States Code with respect to visual depictions of actual sexually explicit conduct are kept by film studio manufactures' custodian of records."

Obviously, there are no records to be kept by you, but if you emphasize that they characters are not supposed to be under 18, you should be in the clear.