This whole situation is part of the bigger problem of celebrity/influencer parents who post their kids online. Once those images are online, they're there forever. And you're opening your kids up to a whole world of abuse, bullying, and exploitation, both from people who know them, and those who don't.
But this is a whole new level. It's bad enough when fan accounts, or even just fans, repost images that have been put online by the parents. But by bringing your children onstage, you are allowing an audience of a few hundred people to take pictures and videos of your kids. And I don't necessarily begrudge the audience from doing that - they want to take pictures and videos of the band they are there to watch perform, and their children just happen to be in the photo or video too. But now those people are posting these images on their social media, and what makes it worse is that those images are theirs to post - they took them, they belong to them! In what other context would this be considered normal or acceptable? It wouldn't. If these people weren't in the 'public figures' it would be considered very weird indeed.