Al-’Allaamah Saalih al-Fawzaan (may Allaah preserve him) was asked:
[Q]: Noble Shaykh – may Allaah grant you success – the questioner asks:
“Is it permissible for me as a parent to search through the mobile phone and computer of my children, fearing that there may be something upon them?”
[A]: The Shaykh responded,
“Yes, this is obligatory upon you. It is [mandatory] that you inspect them and look through them. How many times have I mentioned to you that you should not buy them mobile phones that have the capability to do more than [make a call] and speak on them…”
[Q]: The questioner said,
“May Allaah preserve you! Some people say that this type of behavior on behalf of the father is deemed to be spying, which has been prohibited. Is there any truth to this statement?”
[A]: The Shaykh responded,
“This speech is false and erroneous. The parent is commanded to nurture and educate their children, supervise them and to monitor them. It is compulsory for them do this, and this is not considered to be spying. This is fulfilling the mandatory duty that Allaah has placed upon him…”
http://www.sahab.net/forums/index.php?showtopic=134967
Translation by Hassan Somali
Barakallaahu feekum