You didn't do anything wrong !!!
It was an open place ... full of people ... and some of them were children. You weren't taking pictures of the children with anything but the most innocent of intentions. The fact that one of the children was perhaps a little under clothed is completely irrelevant.
This was not the beach with scantily clad families enjoying a sunny day or a little water park with kids in their underwear running through sprays of water.
The parents, I think, were a little overprotective, but although what they did made you feel bad take some comfort from the fact that those people were doing what they should be doing ... protecting their little ones ... and those of others.
Each of you resolved the situation respectfully ... and it does seem obvious that the woman was not just looking for the pictures of her own children ... but to see if all the other ones were of children too ... and therefore doing what all people should do ... getting involved when something doesn't feel right.
You both did an admirable thing. She was undoubtedly relieved to find that her suspicions were unfounded and left feeling she was good mother and person, and that you were just somebody who's hobby was snapping pictures of the world around him.
You went through it without letting your own 'triggers' lead you into overreacting, and left with well earned dignity.
We all live with the fear that what was done to us might lead us to do the same to another.
Our sensitivities have been warped by those with absolutely none at all ... don't let theirs ruin
Everything that happened unfolded exactly as it should have.
Be proud of how you got through it.