I don't know whether it is because of the growing DINK (double income no kids) phenomenon, or lingering Victorian ideas of kids being seen/not heard, but our society is pretty inhospitable to children in public.
As it relates to children the public sphere is intensely segregated. There are places specially set aside where kids are welcome - matinees of an animated movie, playgrounds, schools, family-friendly restaurants and fast-food joints. But step outside those boundaries and you will hear about it.
I have a pretty rebellious attitude and a thick skin and even I am constantly aware of the rolling-of-eyes, the impatient sighs, and the cruel looks that get shot my way when Curran decides to sing a song in the middle of dinner at a nice restaurant, or Avery turns to ask me a question about the plot during a movie or at a play. To sensitive parents like my wife the scorn is a palpable barrier to participation in adult life. Plenty of parents choose not to go where they know they aren't welcome.
In the short and the long run this attitude is very destructive. Being a parent is hard. No, being a parent is impossibly hard, and we have compounded that difficulty by isolating parents. While we approvingly quote generic proverbs like "it takes a village to raise a child", in fact, we have made children just another individual choice - a commodity. Some people "choose" to have children. Others don't. Since it is an individual choice the individual bears the cost. Why should the single, the childless, and the retired have to endure your parenting trials, the noise, the smells, the inconvenience with you?
I implore everyone to realize that however much the baby on the airplane is making you suffer, the parent is suffering 100x more. If you're conscious of a child making noise in a movie theater, the parent is completely consumed by it. Think it's hard to enjoy your dinner with the rugrats in the next booth bouncing around? Try being the parent.
The solution can't be segregation either. Some people want parents to keep their kids to "family-friendly" environments not just to avoid the awkwardness of having to put up with children, but also to protect the children. The result of this kind of thinking though is to consign parents and kids to ghettos where everything is primary colors and cheesy music all the time. It is bad for the parents, the kids, and society.
First, the parents. Having children doesn't mean we stopped liking music and wanting to go to concerts, or museums, or the theater or whatever activity you think is too adult for us to be bringing our kids to. For sanity's sake we need to continue to engage our interests and passions. Doing so makes us better people and better parents. Leaving the kids at home is not always an option and even if it was, one of the worst things a parent can do is exclude their kids from everything they like to do in life. Not everyone has the same ideas as you about what is "kid-appropriate" (an idea I think is flawed to begin with). Try being less judgmental about what a parent should or shouldn't be exposing their kid to - especially if you're not a parent yourself.
Next, the kids. Segregating kids from adult activities is bad for them. Kids learn to like and understand adult activities by being exposed to them. If you think it is an inappropriate environment for a child, instead of making a snide remark about bad parents, try doing your part to make the environment better. Talk to kids. Explain what is going on. Look out for them and help them, rather than ignoring them. You know what makes an environment unsafe for kids? Adults. But we could just as easily make things better rather than worse.
Finally, society. No matter what you think, raising the next generation is your responsibility as much as anyone else's. We are shooting ourselves in the foot if we continue to cut parents and children off from the elderly, the single, the young, the employed, and so on. We should be doing the opposite. We should have children in the workplace observing and apprenticing. Children should be present at every important meeting of government and business transaction, in every dance club, bar, theater, museum, warehouse, and factory. Far from us teaching them bad habits (which we already do quite well), they might actually teach us a bit of restraint and compassion. There might be less corruption, greed, lust, and hatred if we had to do it in front of innocent eyes.
Jesus said "let the children come to me." We say, "yes, let them go to Sunday School, or Day Care, or the playground or somewhere else away from me." Children are loud, and inconvenient. They don't follow the social rules. They interrupt our lives. They are inconsiderate. They get hurt and they cry. They find something funny and they laugh without regard for who else is listening. They are also people. Not someone else's responsibility. Not someone else's choice. Human beings. Who are especially in need of your care and attention. Quit rolling your eyes and say hello.