No. It's not okay, because the children did not consent to be murdered.
Can a parent consent for the child to have sex? Of course not. A parent can't sign their child's life into debt.
Parents can not consent for their children, especially when that consent entails being conscripted into military service, taxed, and being put in prison for possessing a plant.
You should re-read Hobbes. Outside the social contract we live in the natural state of man, where our rights are to do whatever we think necessary to ensure our well-being, no matter the consequences to anyone else. Without a state, from where do you derive the right not to be murdered? The strength of your own limbs, and little else.
> A parent can't sign their child's life into debt.
Student loans aren't actually very far away from that. (Not everyone taking out a student loan is over 18 or the local age of majority, which I realize that you haven't personally consented to what that age of majority should be.)
Instead, of course, we discover that parents in fact, sanely consent for children until those children are capable of consenting or not consenting for themselves.
We also discover the concept of implied consent, whereby people using the benefits of a contract have also consented to the burdens.