Open the doors for the things that are age appropriate and support their efforts. Finding that balance is impossible. Bottom line is that if you don't know where your children are, you may someday regret that lack of knowledge. If you can not learn to turn their mishaps into positive learning experiences, the mishaps will continue toward bigger and better mishaps. Knowledge is powerful and useful.
Ignorance is NO excuse.
Be it on the Internet, at the library, on the streets, or in the malls. A resource site which provides further information that might prove useful, and a few of the cyber sitter type sites that have been around for a while. I don't personally endorse any of these products. As a note of concern. Please understand that it is VERY likely that any or all of these packages WILL prevent sites that are not offensive to you or your children.