My neighbor in a Condo development is harassing my boy saying he goes on her lawn which is common property. She is upset that the children run wild (son= 12).
She sates she is calling the police.

So let her call, if your son is not doing anything wrong there should not be a problem

First, you need to tell your son to try and be respectful of the neighbor. But if she is being totally unreasonable, then let her call the police and they will tell her to chill.

If the lawn in question really is common property then she has no case as far as that's concerned. What exactly is your boy doing when he runs on the lawn in question? Make inordinate amounts of noise? Tear the lawn up? Damage peoples' personal property? If he's not breaking any laws then calling the police would be a total waste of time. She may decide to complain to your housing association. And that's actually what she should do if she believes that she really has a beef. Otherwise I'd just hang low and not worry about it. Meanwhile you may want to check with your association yourself to make sure that the lawn in question really is common property. Just don't drop any hints that your inquiry is based on a dispute with a neighbor.