Think about what you're proposing. You want me to drag my son, a kid who was little enough back then to still ride a bike with training wheels, into a tense argument between a weird lady, some scary-looking adults, and his parents who suddenly decided to lie through their teeth for some reason? Aside from what example I would be setting for him, how do you think a kid would handle a situation like that?
It wasn't enough that this lady already pissed on his parade, I'm supposed to compound it and put us all at risk of having him taken away because we were "negligent" and also falsely accused someone of being a pedo?
Have we forgotten that the #1 priority in this whole situation is the kid, not our pride or out desire to put someone in their place?
You don't know this person. A little old lady is unlikely to be a child molester statistically but it has happened. So when the cops knock on your door, maybe that's the concern that leaps to the front of your mind. Don't accuse anyone of anything just mention details, for example perhaps she touched him on the stomach to stop him "she placed her hand near his penis". Get creative. "Obviously a sensitive topic like this can't be discussed in earshot of the child victim".
You may say "I want to do the right thing" and that's fine, but personally I want the right thing to happen (ie. Kids being allowed to play outside) and I'm willing to bend the rules in the very same way that the people trying to prevent that are.
The #1 priority should not be the kid.
The #1 priority should be the benefit of all kids.
In this example risk is introduced to the custodial relationship of the immediate child for the hopeful benefit of all children. It's possible this could be a rational risk. Whether it would be effective I have my doubts.
If we use some arbitrary numbers perhaps it would be just to risk 1/1000 chance your own kid gets tossed in foster care by CPS if it means 10 unknown kids end up with 10% longer lifespan because they built healthy habits by being able to play alone outside because a threatening old lady got put in her place.