I think poor parenting is the problem. I love kids been looking after kids for decades but I am increasingly seeing poor behaviour not being managed or even noticed by parents - and I'm not just talking annoying I'm talking potentially dangerous to the children!
Letting children run riot crashing into tables in cafes/restaurants where there's hot liquids and sharp knives about, letting them run in and out of church doors when the church was on a main road, playing on escalators, climbing on shelving in supermarkets especially worrying in an aisle of glass containers...
Also potentially harmful behaviour around frail elderly and disabled people - bumping into people using walking frames, ramming wheelchairs with push along toys, "cutting up" people walking eith sticks or crutches.
I wouldn't have allowed any of my mindees or my dd or her friends (eg with us on days out etc) to behave like this.
Yet I see it regularly now and if you dare say anything to the parents you get a barrage of abuse!
I've even had a parent scream at me for stopping their child run into a busy main road and almost get run down!
The library thread the op refers to I almost posted on.
It wasn't just children being welcomed, it was an unrestricted poorly planned play area just plonked in the library. Totally inappropriate. Libraries don't need to be silent but quiet and calm yes. The op of that thread was trying to study, that's a normal valid use of a library, as is reading, doing research and these days many are needing to use libraries to access benefits and apply for jobs which requires a level of concentration hard to achieve if a lot of children are playing loudly nearby (the play area had been put right next to the computer bank iirc).
Yes children should be welcome in most places BUT they should also be taught how to behave in different places.
Proper play areas, soft play, parks, sports and leisure centres - run, jump. play, be loud, shout laugh loudly etc
Church, library - sit and be quiet and respectful
Restaurants, cafes - chat, laugh fine running around potentially causing accidents and causing stress for other customers and staff - no.