It isn't completely compatible though. If God is omniscient we can't have free will because we can't make a decision different from God's knowledge. One thing negates the other.
God knows but we don't know what he knows. We're free to make whatever decision we want.
We'll take Hitler as an example. If God knew Hitler was going to attack the jews, and knew everything else as well, then it stands that God is omniscient. That means that God knew millions of years ago that Adolf Hitler would attack the jews and everything else that he did. How could he have possibly chosen to do anything different?
God's knowing what Hitler would do didn't negate his free will.
If he had, then God's no longer omniscient because he didn't know that Hitler would do something different.
You can't have an all-knowing God and people with free will. Your example of your son doesn't hold up because you're not all-knowing.
I'm not all-knowing, but in the analogy, I knew with certainty how my son would react in that situation.
(Sorry if this doesn't make a lot of sense, I'm getting tired

)