I have a feeling I'm going to get toasted to a perfect 'well done' shade of brown here.... 
I went to the library with DD today, and as we came in, there was a woman with a pushchair standing at the desk. As I was returning our books (not at the desk) and browsing, there were two children running around, screaming and shouting - the younger boy looked about three, the older boy five or so. They seemed to be with the mum at the desk, as she occasionally ssshhhed them (of which they took no notice at all). There was an older boy who looked to be six or seven, who joined in with the shouting and running from time to time, but wasn't causing the same chaos as the littler ones. The toddler had an utterly ear piercing shriek (I really can't stand shrill noises, so I realise I'm less tolerant of this kind of thing than many people), which he was letting rip frequently and very very loudly. There was a bloke there who I presumed to be their dad, as he sometimes spoke to them and called them over, but they didn't pay any attention at all, and he didn't push it or try to moderate their behaviour.
I joined DD in the children's section, and the two boys were running in and out of that area (then across the library to mum at the desk again). They were fighting, very vociferously, over a bottled drink, a fair bit of which got spilled on the floor. Several books were also knocked onto the floor. A couple of other children were sitting on the covered seats/cushions, and were intimidated by them rolling around, shouting and fighting. I was feeling very 
and wondered why the staff didn't point out to the mum that this wasn't ok behaviour.
As we checked our books out, the toddler screamed very loudly right behind me. I said "God almighty" and turned round, and the mum was walking past me with all four children. She said "What?? He's only two". I said "They've been running around screaming and fighting for the last twenty minutes. This is a library". She said "I don't care" to which I replied "Clearly; if you cared about other people, you wouldn't let your kids run around screaming and fighting". The woman walked off to the children's section.
I thought about what had happened, and thought maybe I'm completely out of sync with what's acceptable in libraries these days. As I was leaving I went to the desk and said "I know libraries aren't the solemn, silent places of the seventies, and I'm really glad about that, but is that now acceptable behaviour for children in a library? Am I way off the mark on what is ok?". The librarian said that the woman was joining the library, and that she had four children who'd never been in the library before (one was a babe in pushchair, obviously), so they didn't say anything to her. She looked quite at me.
I can see her point, and am wondering whether I was BU to say what I did. But to me, wherever I was I wouldn't let my children run around fighting and emitting ear-splitting shrieks, let alone in a library. I know it's not a sacred sanctum, but a library is supposed to be someone where you can go for peace and quiet to enjoy books.
So AIBU?