Personally I don't have any concerns. This is the way the world is moving, and the kids need to get on board pronto.
True, but our laws haven't kept up. One example is that anything that is published on google + is treated as a 'publication' , so I wonder who is liable for any defamatory comments that maybe made. It does essentially give kids as much as a voice as adults. Also could be used against kids in future jobs, as checking peoples online footprint is what employers now do. A lot of kids do some pretty stupid things from time to time. Once something is online, it's out there forever.
Maybe they should have a google+ / facebook system just for kids, so only people under a certain age can view those posts.
Nice idea, but again open to abuse (e.g. pedo's signing up as a 13 year old looking for a special friend)
I don't think an employer is going to be to concerned about an 11 or 12 year old online comments. What this comes down to is education, much like the old "don't talk to strangers". Kids need to be taught how to use the internet wisely and safely and protect themselves.