This is a very interesting discussion. In my personal opinion, I completely understand if they need to find proof if the child would end up being dangerous or not, ( if it was me I would look until there was no other way), but if they child is proven to be dangerous and can harm other people...he needs to be eliminated.
its sad, but its about saving other innocents. Of course bringing the whole "should they or should they have not killed Sam along time ago" is quite complicated and head-ache worthy.
This is all spectulation but i believe they will end up keeping the boy alive thanks to their good hearts and end up regretting it later like Jus in Bello. But that is just spectulation.