If you didn't allow them to believe that you were somehow connected to L'l sis, how did you get them to give you any information regarding her?
That is where I think that you possibly made a big mistake. There was nothing wrong with calling them to get information about their classes and times and dates, but once you asked a question about someone else's child, you crossed a pretty big line. I wouldn't have done that.
Think about it? Lets say you get married and have another child. If the ex made calls to outsider organizations etc to try to get information regarding your child, what would your reaction be?