To be fair, they're passing mad laws tho. In Canada, it is now illegal to have "Lolicon" comics or games depicting minors. In the US it goes by state by state tho most of the people who have been convicted of owning comics/drawings/games have already been convicted at some point and are on a registry but this is not always the case.
At the state level, some states have laws that explicitly prohibit cartoon pornography and similar depictions, while others have only vague laws on such content. In California such depictions specifically do not fall under state child pornography laws, while in Utah they are explicitly banned.
Best bet: Have the user create the ages, which I have been seeing more and more.