As an added note: just to protect them (all three of them) from malicious code (read: virus, etc), I kindly asked that any time they want to install an app, they should please let me first check whether the app in question is "safe".
They all either have/had laptops or desktops: so this was a no-brainer. Also, since they all use Macs, I can actually limit installations to "AppStore". So, normally, if they find something in the Apple AppStore (OS X), they ask me to check if it's ok or if there are any known issues with the app in question, and then they can install (or I remote-install). In case of non-AppStore-apps, I ask them tobe patient until I check the app and then they can install. It actually works quite easily.
Of course, nowadays, my daughter does everything by herself - but when she's unsure about any security-issues with an app she wants to install and can't find enough information about it on the internet, she still emails or texts me...
I saw a comment somewhere in the comments that it is also very important that the children can always come to you if they find something troubling - without being afraid of being reprimanded or so - my experience was the same: this was very, very helpful and fostered the trust even more. And what is more: the children (the three I'm talking about) also had a feeling that, if they did something I wouldn't "approve of", that they would be misusing my trust - this actually made my life way easier than anything else (they jut didn't want to disappoint me...)