You could also say: "my life's reason" but it is still a bit unclear. "This is what I live for." would also work given that they are his children. But in any event, "the reason of my life" is your worse choice. I suggest you think about it and do an edit.
Well, it may be necessary unless you don't mean a specific God, in which case you would say god...but if a specific God was intended, it would be with a capital letter like any proper noun. So which one was it? The real one or just any old non specific god who doesn't exist?
Hey gang...I don't care if every one of you vote for "The reason of my life", it is not correct English and I will not validate it...in fact, if I don't get something real I will reject it.
I agree with David. "The reason of my life" is NOT correct in English. If there's some reason why you don't like "The reason for my life", you could use "My reason for living".