The first step, I believe, is to consider what the question actually means to the person. The answer, "Because God has given us free-will," whilst correct, is so simplistic/trivial and academic that it's of no use.
So let's consider it:
Person: "Why does God allow suffering?"
By which they mean: "Why does a God of love allow suffering?" (because of course if they believed God was evil the answer would be obvious)
If the person is asking genuinely, this probably actually means:
"If God loved me, why did He allow me to suffer as I did?"
implying that:
"If I had God's power, I wouldn't let innocent people suffer."
and maybe in their case:
"If I had God's power, I would defend the children in this world from abuse."
To be continued... !
