I have a six year old and yes it being summer we let her stay up a lot later than we do during the school year maybe even until midnight but this movie would have let out around 3AM and that is way too late for kids that young to be up even if is summer much less in a crowd of rowdy and noisy movie fans. If you have ever spent much time around a child who was very tired but unable to sleep you would know how unlikely it is that they would be well behaved. Older kids maybe but kids who still were having accidents in their pants and needed help getting dressed just a year or two ago (or even sometimes still do) aren’t ready and don’t need it. The parents aren’t taking the kids for the kid’s sake they want to go themselves and are dragging the kids along. Being a parent means sometimes you don't get to do the cool things like go to the midnight openings of Batman movies. As you mentioned it is summer so if you really want to take your kindergartener to see the Dark Knight have some sense and take them to the manatee when all the other kids will be there and leave the midnight shows to the teenagers and twenty nothings.

I have no idea how old you were when your mom was taking you or how late the shows were but did she have you at crowded movie openings at 3AM?

Now taking an infant is both foolish and selfish. The time doesn't matter but the noise would have most any infant screaming and crying before the movie was a quarter way through. The parent who isn't smart enough to not have brought the baby to begin with is probably not smart enough to actually leave when the baby starts to cry and will spend five min standing near the exit bouncing the baby in a futile effort to quite the baby annoying everyone else before and usher finally ask them to step outside. Infants shouldn’t be at movies in general but one where to loud for them to sleep is stupid.