"Or is it possible for me to put a dog down and it not be murder?"
Is that really the same as killing little children in a worldwide flood because you screwed up in your creation?
Your question has a mistake in it.
Who says "God" screwed up?
The idea is that humanity chose depravity. God came to fix it.
So, with that correction, Yes, God is not a man that He can do wrong, and God will do what is right with creation when it gets out of line.
Your life and mine, for example, are His to end if He deems it necessary.
Perhaps you think Truman was wrong to nuke Hiroshima and Nagasaki?