This requires a broader discussion on the problem of evil; the logical formulation thereof, which attempts to show that the central doctrines of theism are fundamentally inconsistent with one another, goes something like this:
Premise 1: If an omnipotent, omniscient, and omnibenevolent god exists, then evil does not.
Premise 2: There is evil in the world.
Conclusion: Therefore, an omnipotent, omniscient, and omnibenevolent God does not exist.
The argument is logically valid, and since no theist really disputes P2, the soundness of the argument as an atheological proof rests on the validity of P1. The logical formulation above is not considered a convincing argument by professional philosophers of religion, theists and atheists alike, due to the following possibility: God has morally sufficient reasons for permitting the existence of evil. There are no good epistemological reasons to deny such a possibility thus as long as that additional premise is logically plausible, then the logical PoE fails as an argument against the existence of God. We don't HAVE to know what those morally sufficient reasons could be for that premise to be true.
I admit this is unlikely to satisfy people emotionally, but it is what it is.
This is pretty much a huge problem with masses of so-called 'solutions' to it, but the mere existence of evil does not prove God doesn't exist - just that this God clearly isn't a very loving one (though once again there are arguments against that).
Perhaps there is a God who is just a really disgusting being/
I guess maybe God wanted them to born like that to be used an inspiration for others and bring glory to him? If we're going to go "why do bad things happen" route, this world is ruled by Satan.
You see, in order for us to have free will, God can't control everything for us. But the main thing for us as his creations is not to ask why?, but just live life as a good person, to test your faith despite any challenges that you have or your loved ones have. The life we have now is just temporary, in heaven we will be free from disabilities, pain etc. and be away from the materialistic world.
Remember God created the universe, so we can't expect to understand his thoughts and plans. Our understanding of the world is just ultimately limited to our 3 dimensions, but God is beyond that. Therefore, just aim to live a good, happy life, and care for another etc. and don't just keep feeling anger or hatred when you don't understand how things work... because that's just life and we are only human.
That's just my belief.