God doesn't give a rat's @$$ about people. You just need to look in his book to see that. He was happy to drown everyone on the planet. For what? What could they have done that was so bad that full scale genocide was the answer? Passover, the systematic slaughter of every first born in Egypt. An act that is greatly celebrated by the Jewish faith. Why? And even look at the book of Job. An @$$hole of a deity, completely destroying a man's life, just to prove a point.
"We're all God's children."....Bollocks. If that were the case child services would have removed us from His house a long time ago. Rant over.

Most common response I get to that question is "whelp.. god works in mysterious ways..."

I just want to slap the bejeezus out of them and when they ask "what you do that for?" I can reply with "whelp, god works in mysterious ways..hurr durr."

Difficult question... And the answers are not easy or clear. One thing seems certain period when one has been brainwashed since a child. That belief system is so deeply ingrained it is very hard to get them to think for themselves. If you use science, logic, and Common Sense. You'll end up with a draw at best cuz they're working on faith period and told to believe in the unbelievable. In fact they feel they will be rewarded for it

Keep asking the tough questions like this one

That is a question that you will find answered within yourself in a little time and dealing with it more. Read all you can about it and soon you can shut them down in a few sentences.