How to best soothe a child whose parents are undergoing separation/divorce?

The child is my son. He’s too young (<5) to articulate his feelings but I can tell that he’s aware of this change and has been sad and mad for being “at mommy’s house” or “at daddy’s house” without being able to go to the other place when he wants to.

How to soothe him? Is there a way to minimize the damage?