adult, streaming services, etc. You can set a time when they can be on the internet as well. Example below shows the ability some routers to block content and even get more granular. What the children will see is nothing, a warning and for your daughter (parent) she can look at logs as to what device was accessing sites (thus addresssing issue one on one). 

Anyway, this is for wired and wireless connection. For mobile devices with data, there are apps out there as well.

<input style="box-sizing: content-box;" type="checkbox" />Adult

Block adult/mature content to prevent children from visiting sites that contain material of a sexual, violent, and illegal nature.

<input style="box-sizing: content-box;" type="checkbox" />Instant Message and Communication

Block instant communication software and messaging apps to prevent children from becoming addicted to social networking sites.

<input style="box-sizing: content-box;" type="checkbox" />P2P and File Transfer

By blocking P2P and File Transferring you can make sure your network has a better quality of data transmission.

<input style="box-sizing: content-box;" type="checkbox" />Streaming and Entertainment

By blocking streaming and entertainment services you can limit the time your children spend online.