What weight has the kamma when forced to do bad things as a child?

Example: A child (+/- 8yrs old) is forced to kill an animal. It doesn't want to, but has to because it is threatened by abusive adults. Wanting to kill or not doesn't, I think, matter when it comes to the bad kamma performed here. And yes, since it is the child that performs the killing, the bad kamma is done by the child and the child will bear the negative results of that kamma. But, what about the weight of that kamma? Since the child had no option but to obey. How heavy is that kamma? How heavy can the results be? Does anyone have an idea (preferably with source to text in the Pali canon)? (Related: https://buddhism.stackexchange.com/questions/9716/what-is-the-buddhist-perspective-on-child-abuse/25950#25950 . Except that that question was about the cause, mine is about the weight of kamma.)