This is something I think about a fair bit. What triggered this post was G+ opening its doors to 13 to 18 year olds.
In this country we have an obsession with protecting anyone under 18 from exposure to 'adult' material. (Never mind that the age of consent is lower than 18 in some states. The UK also has the same stupidity - you can legally have sex at 16 but can't watch a porn movie until 18).
Now, as far as it goes, that can be dealt with. Porn shouldn't be on open networks anyway - it should be clearly marked so that those who want it can find it and those who don't can avoid it.
However, many parents consider anything related to homosexuality or gender issues to be 'adult material'. I seriously know of parents who don't want their little darlings to know gay people even exist.
Frank discussions of abortion and related issues? Definitely 'adult' material. Because of this, the presence of minors can have a chilling effect on speech.
Unfortunately, the obvious answers don't work. You can't mark the profiles of minors as such without letting the predators know exactly where to find them.
I personally will not dumb things down because there might be minors present, but this probably means uncircling and possibly even blocking people I know to be under age...not because I feel what I say is unsuitable for them but because one parent might. Even if that parent is doing something I consider unhealthy, I have to respect them.
On the other side of the coin, I like talking to teenagers. They're often a fresh breath of air. I don't want them to be barred.
I like the suggestion another user proposed - the ability to mark posts as 18+. The problem is, that Google probably feels that their ban on adult material/nudity covers it. It really doesn't, just because some parents are overprotective.
Well. We keep plodding along, I suppose.