|If you want to permanently disable inprivate browsing so that no employees can hide from you what they were doing on the internet, go HERE for instructions on implementing it through GPEDIT.|
If you have determined kid(s) that is(are) driving you up the wall, I can understand why they love it. When in an InPrivate Browsing session, no cookies are created, no temporary Internet files, no history, no form data, and anything else that a browser would normally record for you to check on them.
You can permanently disable InPrivate browsing through Windows 7 Parental Controls features. Start HERE then exert your authority as a caring parent(s)