Is it necessary the object of 近づける movable? Assume that there is a pond in the garden in which a boy is playing around with his father. What is the correct expression that his mother must use? * A: Keep away the son from the pond. * B: Keep away the pond from the son. My feeling says that I have to use A because the object of must be movable. Is my understanding correct?

Yes, your understanding is perfectly correct. You have to say A because Sentence B sounds like is a movable object.

Well, this is off-topic, but addressing one's son as is weird. See this.