<blockquote><b>Quoting Jude ♥ JGL:</b>" <blockquote><b>Quoting Niklaus:</b>" Yeah, that is probably the biggest argument. ... [snip!] ... be what people wanted though? Yes, a lot of people were killes but it could also change a lot of things about modern times."</blockquote>
True. And in the scenario of the OP, I'm sure a lot of things would change with the death of that child also.
Something else I thought of is that if they 'knew' ' the kid would kill someone, then they must know circumstances. When, where, why, how. Morally and logically speaking it would make more sense to wait until the intent was clear and step in to stop it.