This is something I would speak to an attorney in your area about. If "Swim" is a criminal and part of an investigation, it's possible the police may have been able to legally enter your house if they had reason to believe he was there. I know don't enough about "Swim" with the information you provided.
Going on the facts and story you provided, it seems as though the police entered your home without permission. Unfortunately, a recent U.S. Supreme Court ruling out of Kentucky states that the police are now allowed to enter an individual's home with or without a search warrant if they hear noises on the other side of the door coming from within the house. I believe this ruling was made to prevent people from destroying drugs or evidence before police can seize it. Perhaps the police heard you and your girlfriend moving around inside and decided to make a move.
I am in no way an attorney. As I understand it, police almost always need a search warrant, permission from the owner, or illegal contraband in plain view to just come into a home. This could be different depending on the laws in your state (of which you should ask a lawyer about), but, hypothetically, even if your little son happened to open the door, he is not the home owner and therefore cannot give permission.
This article outlines, among other things, when search warrants aren't needed when authorities enter a home. Though your house wasn't searched, it appears the police wrongfully entered your home. I hope it helps.
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if you truly feel you were harassed by the police, speaking with a lawyer immediately might be the smartest option. Good luck.