The answer, I believe, doesn't lie with us. It lies with where the children lived. See, the people in Maddie's neighborhood knew how not to let people forget. But many of the people who were around when Bilalian and Yvonne were killed are no longer there to remind anyone. Which is why we have to start to rebuild neighborhoods economically and socially if we ever expect to place a high premium on the lives of all children.
Stability helps neighborhoods seek justice.
It emboldens them to make the world pay attention. To not let the matter drop. Transiency and poverty do not. Their killings were so savage that police wouldn't release details. Like Maddie, they were last seen alive in the midst of the most innocent actions.