Is it destiny?

Tonight I was sitting and listing to a minister talk about free will vs predestination. As this was being discussed I had an idea! Ok, this may be lost on some, but just follow me here. Parents seem to ALWAYS know what the children are doing or are going to do. Sometimes they step in, sometimes they do not. Well it is not that the child does not have the free will, but the child will act in his/her nature. Well how much more will God know what we are going to do. I mean if earthly human people know that you are going to do X then why can't the heavenly father know we will do Y?