My older children have mobile devices, and while they agree to allow us access to them and installation of software to permit us to review how they use the device with them, they also work around those measures and prevent such systems from working well. For instance, play games when they shouldn't be (middle of the night, staying up for hours, not getting up on time, etc), and occasionally obtaining games that they are not allowed to play at their stage in life, among other things.
They aren't very good at keeping this out of sight, and so occasionally a younger sibling will see something that is disturbing for them, given their stage in life. Some of the media they are playing or watching have levels of violence, relationships, or language that isn't appropriate even for the teen, but certainly not for the younger child.
While we are tackling the problem with the older children separately, what I'm trying to figure out is how to encourage my younger children to discuss these things with me.
There's a lot riding against that - they feel it'll be tattle-telling, what they've seen makes them feel yucky, unhappy, or guilty, their older sibling has cautioned them against it, they feel like they might get in trouble with us or the sibling, etc, etc, etc.
When they do tell us, it's relatively easy and painless to explain what they saw, help them understand how it relates (or not) to them and their life, and give them relief from the anxiety it may have caused.
How do we encourage young children to discuss disturbances with us, overcoming the various barriers that prevent them from doing so?
While there is a lot that could be said (and has been said) regarding mobile device usage and tracking, and that is one possible source of disturbing media for children, please do not focus on this. They could have been shown disturbing images or stories by a friend in school, or protestors on the side of the street, or even some relatively benign subject was discussed that is new and unfamiliar with them. The technology aspect is my particular situation, but please focus on resolving the fallout, not on preventing the initial exposure.