I totally agree, aquinas. The more I think about it, the more frustrated I get. I genuinely wonder whether a free public library event can actually (legally?) forbid someone from joining...
I understand our frustration Marnie but I would save my passion and frustration for other situations, and I'd also try to look at this from a different angle than simply young-gifted-child can't participate due to age. If this was happening at school and impacting your child's education, that would be something worth fighting for, and depending on the circumstances, possibly something you could make a legal argument against.
I also think that leading a group activity yourself is a great idea - not just for making the activity available for your child and for others, but also because it will give you the experience of planning and leading an activity for a group under similar circumstances. I've led quite a few group activities for children, and as the person who's doing the planning, you'll put thought into who you are trying to reach, what you want to do, how to execute the plan etc. I think it might help you see this particular experience through the eyes of the person who's leading it - while it may not make sense to you that she excludes children who are under 7, there is likely a reason she's planned the age range that she has and even though you don't agree with it, I'd try to respect that it most likely wasn't a thoughtless decision on her part but a purposeful decision. I suppose that can be construed as essentially me saying I'd give this person slack that I wouldn't give the school district.
It would have been so easy to leave, if it there were any issues. So what is the harm?? That's what I don't understand.
It would have been easy for you to leave, but the other kids might be distracted by it, it might have taken time away from the work that the instructor had planned, it might distract the instructor's attention, it might take away the enjoyment and enthusiasm the instructor had and was conveying to the other kids who were attending. I think it's important to remember, this is a one-time event that is short in duration - which means it may not seem significant to you in terms of giving your ds a chance to attend, but it also means it's a one-time event with short-duration for the person who is leading it (and who is likely putting a lot of thought and planning into it ahead of time). She also doesn't know you and doesn't know that you'd "just leave", and she doesn't know that her idea of when that "just leave" moment has occurred is in sync with your feeling of when that "just leave" moment occurs. Those are all things that may be weighing into her decision.
I think I am going to tell DS that the class was cancelled, since I don't want him to become troubled about the circumstances surrounding his not being allowed to go.
Another approach is to let ds know that he wasn't old enough for the age range that the class was slated for, that you thought he would enjoy it anyway so you asked if he could attend, and that you were told no. Keep it simple - let him know you advocated for him. Advocacy doesn't always work, and you don't need to let him know you're upset about it, but it's ok to let him know that there was an age range on the class and he didn't get in because of it, but that you as his parent did ask. He's going to appreciate over the years all the times you'll stand up for him and advocate for him

Best wishes,
polarbear