It is a difficult subject. Like Stacey’s children, I loved running through the adult sections when I was a child. Looking back, I think I spent more time in the adult sections than the children’s. I think the designated spaces are a wonderful idea but some libraries may not have the space to do so. It is not just children making the noise, my local library has “Learn to use an iPad” sessions, in this situation the lecturer has to speak loud enough for the group to hear but be mindful of not being too loud to bother other users.
As you said, there is no ‘yes or no’ solution but I think regular library users learn to avoid peak time for children. For example, when I was swimming laps I learnt when the Aqua Aerobics classes where on because it was remarkably difficult to swim laps during those times. Likewise, regular library users might learn to avoid the library during Storytime and after school. Libraries need to cater for the young and old, and I think most people can accept that.