Mrs C and PA have given brilliant thoughts on this as usual. It is such a difficult question and something we can never have 'the' answer to. It is all bound up with the fall and the broken world around us, yes, and sin and effects of sin. But that doesn't make it any easier, especially for the victim.
The Shack is a good read on this (though agree not the most literary work!), also 'The problem of pain' by CS Lewis and as MrcC said 'where is God when it hurts?' by Philip Yancey. Another good book is 'God on Mute' by Pete Grieg. I am doing quite a bit of work on this issue at the moment, from the perspective of living with chronic illness - why doesn't God intervene - why not heal everyone? I don't know.
I do know that God is in it with me, in the pain, and that yes, somehow he is in the pain with those children. Why he doesn't stop it is a mystery, and hard to grapple with. We are never going to have an answer here that satisfies non christians, I'm afraid, but we can with integrity share our beliefs about God being in it with us. I love the Message translation of John 1:1 'The word became flesh and moved into the neighbourhood'. Jesus came into this broken world and lived it with us.
Sometimes God heals. Sometimes he stops the suffering. Sometimes he intervenes in great power.
And sometimes, most of the time probably, he doesn't.
And yet I believe God is just, I believe he loves the sufferer so deeply that love goes deeper than any pain and anything the abuser can do.
I'm sorry that I don't have a more 'pat' answer to this. Then again, if it was all nice and easy, no one would have an excuse to not believe in God, and there would be no faith, and trust and belief would be worth nothing. IYSWIM.