Speaking as someone who works in the security field, and also occasionally has to deal with irate people about HOA matters--
If you were concerned about the child, then calling the police was absolutely the right thing.
You are under no obligation to endanger yourself by going over to investigate. You have no idea how they would react, or how armed/irrational they might be. Not to mention, if there *was* something going on, the family does not have to open the door to you, or let you in--they can simply lie to your face and tell you to get off their porch. They can't do that to the police, who are obligated to investigate further and can make entry if they suspect anything wrong. And if you did go over, chances are good that you might get screamed at, or worse, for daring to suggest that something might be going on (or even that you object to the noise)--regardless of whether or not anything was wrong with the kid. Plus, now those neighbors have identified you as a potential enemy--and if the police DO get called down the road, even if it's an anonymouse call by someone else, you are suddenly target numero uno for retribution, threats, etc.
The fact that the father canvassed the neighborhood until he identified you, then came and made (vague, nonspecific) threats? BIG red flag. At best, he's a bully. At worst, he's something else. I hope your apology (which you shouldn't have had to make, IMHO), does keep the peace. But if it doesn't, don't hesitate. Call the police.
