The reason why it is illegal to have sex with kids that age is because they are considered too young to make a sensible decision about what they are doing .... would you disagree with that?
No I wouldn't disagree at all.
Therefore you will argue, I suspect, that they are too young to make a sensible decision about making someone a sex slave or about murder.
I will argue though that these things are poles apart. Not being old enough to make a decision on whether to have sex is NOTHING like being part of a premeditated sex ring that takes planning, grooming and ultimately delivery. The two little cunts that killed a two year old boy in Liverpool were not old enough legally to decide they could have sex, but they managed to carry out a planned abduction and murder.
Morals aside, the law is based on an assumed naivity but these actions are far from naive.