I understand OP. Suffering is incredibly difficult to understand and to reconcile with faith. It's the age old question of theodicy.
However, I remain a Christian for many reasons. My experience is that God sustains me in my own life of pain (long term lung diseases which can cause horrific suffering at times, since infancy) - knowing that the God I worship understands because he didn't stand apart and simply look down on us with detachment but became incarnate and suffered the worst of pain and death. I know that this stuff can sound nonsensical - I get that, but it's my experience and the experience of so many billions over the ages that encounter with and relationship with God is not only a sustaining place, a comfort to get through life, but draws us to our utmost purpose and fulfillment in life.
Most of us intrinsically know that suffering and evil is wrong, that these things are not the way things are supposed to be. We are appalled by the suffering of children in particular because we know that it is wrong, it is off, it is an anathema. How do we develop this intrinsic knowledge of good and evil? If we were products of a blind, indifferent universe with no morals then we would surely not be so utterly repelled by what we see as the immorality of suffering. Evolutionary process counts for something of this of course in terms of our will to survive and thus some form of morality within this but does not sufficiently explain our deep seated understanding of the pain of evil and our response to those hurting who have nothing to do with us or our 'tribe'. We understand that suffering is appalling because it is, because there are moral absolutes which govern the way we live. (These absolutes are sometimes dimly expressed in certain societies and more openly in others, and I would argue that much of the modern way of thinking about evil and suffering is founded on principles established by Christianity, with much evidence for this - check out the (agnostic) historian Tom Holland for some excellent work on this.)
Thus the fact that we can recognise good and evil means that we are created for good. The fact that most people lean towards good deeds rather than bad points to a leaning towards how we know things should be. The Christian belief is that one day all things will be restored to how they were supposed to be, but that while we have free choice God cannot interfere with that without being a dictator. If we were created for perfection, with no possibility of going wrong and thus no suffering, we would be pale imitations of humanity in all its glory, robotic beings at the beck and call of a God who doesn't actually care about relationship but only creatures there to do his bidding. Instead Christians believe God created us with intrinsic choice for good or ill, for relationship with the creator or the choice to reject that. It would not be a loving act of creation to form creatures of unthinking servitude.
When we bring a child into the world we do it because we want to form relationship and love that child, hopefully, and encourage them towards fulfilment in life. We do not keep a child chained in away from the world so as not to allow them to make their own bad choices. We have to allow their free choice as free agents, and be there encouraging, loving and teaching. And if they do fall off the rails we are still there, ready to welcome them home and love them. Much as God acts with his creation: allowing freedom, which means evil, yet always there with open arms.
Philosophical stuff aside, yes, I still believe in God, despite Madeleine, despite Covid, despite my daily lived pain, and my experience is that in my daily prayer and life with God I discover inexpressible joy and peace beyond understanding - even when I don't understand. And it doesn't mean I cannot question the evil - the Bible does, all the way through - just look at the Psalms, Job etc. I can question God and yet find utter fulfillment in God at the same time.
I understand, OP, but I encourage you to think wider even than your pain at this outrage and find God sitting in the midst of it weeping about Madeleine too.