Goog, when you ask parents' permission to take photos of their children, do you also (at the same time) explain that you're a professional photographer and these pictures are for your portfolio (or however you intend to use them -- but not for sharing with the kids' relatives)? Might help clear up some misconceptions, since most parents taking pictures at sporting events are probably taking them for a different purpose than you are.
I don't get their permission to take the photos, because it's in a public place and theoretically anyone can take them; I just can't use them. And I actually don't use them for my portfolio online; I know I have to have a model release, and I don't post the pictures unless I have previous friendship with someone and know the person. (ex: I have a FB friend and got a shot with both of our kids, so I shared that with her). So basically, in the case where I get a great shot and I want to do something else with it, promotional-wise, I get the parents' permission because I know that's the right way to do things.
In the case with the t-shirt dad, I specifically asked the mom if I could use the artwork with her son's picture for my business page and she said 'sure'; it was (presumably) the dad who took it one step farther and got the t-shirts made without getting MY okay. Although now the more I think about it, I think the mom was probably just as at fault as the dad, because she was the one with the access to the artwork/photo, so she had to give it to him. And the other strange thing is that she has a sister (I think) who is a professional photographer, so you'd think she'd have heard a bit about copyrights and permissions from the sister.
And most of the time, I don't mind sharing a photo here and there, with some conditions: 1) I get and retain credit for it (so no copying it off of my page and pasting it on yours, or doing anything else with it, like making t-shirts; share it, don't steal it), 2) it doesn't become an unreasonable request (like the dad who wanted my original or the people who say, "can you take a bunch of pictures and send them to me?") 3) I know you and we have a relationship
that involves more than "Hey, I don't really know you, but take some pictures of my kid because you have a nice camera and I don't, and send them all to me, 'kay? Buh-bye."
So far I've gotten good feedback from the gallery that I did for the sports team.