Sin, what is a sin can you please explain to me what a sin is to you, the Tora and the world?
To my understanding, a sin is as follows, a Person does X or Y that is against the code of the worlds matrix i.e the worlds natural order in sense between Good and Evil.
Let's define that even more. You're walking in the meadow, and you see a homeless man, you can easily spare a pence or two, though you don't, nothing wrong there, this happens for a while, other people pick up on the action, then it becomes a custom and they are seen as selfish people in the small community.
So the person that started it, do a sin, or not? In this particular case maybe not at first, though the repetition is what made it a sin.
The world has a natural order ruled by angles or forces, they define the natural evil and good. This is how the people in the times of Noach and later on got judged, as a sin is a sin ie. an action that creates a negative print or (bad angle) in the worlds codex, this is where the phrase the the ways of the world comes from.
Now, that we have a Tora, things became more organized and harder to refute, or deny. Being so, the Tora states the seven Noahide laws, and it speaks against sexual immorality, though noachs generation were still judged before they received the laws, they were evil In the eyes of hashem so a sin for a gentile may go further than the seven noahide laws as the world/nature/forces will judge based on the outcome of your actions, from waisting seed to murder, gossip, and so on.
This does not mean once you're a jew your free, and just keep the Tora no, this is before you keep the Tora, (Derech eretz kadmore la tora) The ways of the land are before the Tora. There are many interpretations and more than one but not all are right.
The ways of the world is in reference to the natural mihagim or land, you must study where you are in order to apply correctly what you know as a jew in the environment, Or the Tora must be learned in order to learn the ways of the world.(The second is correct to an extent, and that is the laws we learn from the Tora itself- De-oraita) All others are just implications from what they understood... (long story)
So in the end yes, they are liable, And yes when it comes to wasting seed even kids under the age of thirteen are liable and not the parents, this is the only sin I have seen this occur.
Why because life force is life force, waisting it goes against nature and so on.
Hope this answers the your question.