Follow these steps for the new version of Twitter (Feb 2012):
You can't. But you can block people or protect your tweets, but if you protect your tweets people can not retweet them.
To unprotect your tweets go to settings and uncheck the protect tweets box.
You can protect your tweets so that you must accept people to view your profile and tweets.
Yes. There is an option to "protect your tweets" so that only those you approve can view your tweets and profile.
You will receive tweets on your homepage from everyone you follow. Unfollow them to not receive their tweets. To stop people seeing your tweets (except from those you approve) you can protect your tweets from the settings menu.
there wont be one. but there are no age restrictions, so "protect your tweets" so that only people who follow you can see your tweets
You can protect your account so that you must approve who can follow you and view your tweets.
You can't do this. You either protect your tweets and approve people to follow you or you unprotect your account and your tweets are viewable and anyone can follow you.
There's no way to know who has viewed you on Twitter. However, you can set-up your page as "private" to protect your tweets.
There is no way of knowing who visits your profile. If you are worried then you can protect your tweets.
Go to settings and tick the box that says "Protect your tweets"
I don't believe you can set up parental controls, however, you can protect an account and not allow everyone to see your children's tweets. Go under settings and select the "protect my tweets" option. This will allow only his or her followers to see the tweets.