If the penalty in the AOC law is high, it becomes, from point of view of his own security, reasonable for the adult to kill the child. Indeed, to find out that the child is killed, not simply runaway, and to prove that the adult has killed it is much more complicate for the police than to force the child to testify against the adult. If the penalties for having sex and killing are not very different, the "average penalty" (penalty times probability of detection) may be lower for killing the child.
Moreover, psychological investigations show, that people prefer the variant with a higher probability to avoid something harmful even if the "average harm" is greater in this case. Indeed, will you choose 1 year of prison with 100% or 3 years with 50% probability? The majority will try the chance of 50% to become free.
If such things like killing a child are extremely rare (compared with the number of pedosexual relations), this is caused by the pedophiles which prefer to go into prison instead of harming the child, not by the society.
(Mike)
I think, the best way (the only way) to minimize this sort of crime are just penalties which are proportional to the real harm caused by every crime and not too high. Only in this case, the perpetrator may prefer to get the penalty instead of doing something much worse to avoid persecution.
(Mike)
If I correctly remember a posting I havn't saved, in Russia (or the former Soviet Union) after establishing dead penalty for rape the number of rape cases with killing the victim after the rape has increased.
A very natural consequence. It shows that increasing a penalty may be dangerous for the victim. The current peanlties, especially in US, are very dangerous for the children from this point of view.
(Mike)