Some savvy libertarians already realize this and just don't say much about it, knowing that as bad as things are, the moral sensibilities of most Americans still have not rotted to the degree of corruption needed to allow them to easily accept or tolerate adult-child sex. To spare libertarianism early bad press, they are content to let that sleeping mangy mongrel lie for now.
Other libertarians still deny that their idiotic and feeble-brained "consent über alles" philosophy can offer no defense to adult-child sex. But "scientists" have already declared children capable of consenting to sexual intercourse with adults, leaving libertarians with no objective basis to refuse to allow "consensual" adult-child sex.
In time they'll accept and embrace even pedophilia. I won't. But then I'm a bigoted, intolerant, hateful, Christian fundamentalist statist.