We have minor children in the house and we want to limit the web pages they can visit "> open the router's control panel, then check for a Parental Control or Website Control menu (the menu is different for each modem and may not be present). 
Once the menu is identified, we click Add URL and enter the website to be blocked. To make the block more selective (and prevent it from affecting all devices on the network), we can also enter the IP address or Mac Address of the device on which to apply the aforementioned block, so that only the smartphone, the PC or the indicated tablet will not be able to access the site.
For the second method, we will first have to configure third-party DNS with filtering options, such as the OpenDNS FamilyShield, already preconfigured to block practically all sites not suitable for children. We enter the settings of our router again, search for the Internet menu or Internet Network and manually configure the DNS for the entire network, using 208.67.222.123 and 208.67.220.123 as addresses in the Primary DNS and Secondary DNS fields.
By confirming and restarting the router we will now have maximum protection from all websites that are not suitable for minors, without necessarily having to manually configure every single site we intend to block.
If the router provided by the telephone operator does not allow you to change the DNS, we can always connect a new one in cascade and use it to connect all the devices in the house.
NOTE : remember that changing the DNS on individual devices will allow the smartest kids to overcome the DNS block, so we only use this method alongside one of the methods that we will show you below.
How to block a site from your PC
If the child often uses the PC with Windows to play or to surf the Internet, we can block access to one or more sites by installing the free WebLocker program.
With this program we will be able to set an automatic block to pornographic and unsafe sites for minors, add custom filters, automatically choose one of the DNS servers safe for children and set a robust password to change the settings and tamper with the filter action ( it will not be possible to turn off the program or prevent it from starting automatically).
If we want to change only the DNS of the computer with Windows, we recommend you read our guide on how to change the DNS servers of the internet connection on Windows 10 and 7 ; to change DNS on Mac, just read our guide on How to change DNS on Mac .
As an alternative to the program, we can use the free Block Site extension, available for Google Chrome and Mozilla Firefox, directly on the browser.
With a few clicks we will be able to block the most dangerous sites for minors and set personalized blocks on the sites that we do not want to be visited, all seasoned with a security password to be able to modify or remove the extension (watch out for incognito mode, which is basic don't load extensions!).
How to block a site from your smartphone or tablet
If, on the other hand, we want to block a site from your smartphone or tablet (which is very likely, given that today's young people are born with these devices already available) we recommend using the free Norton Family app, available for Android and iOS.
With this app installed on the mobile device we will be able to control the websites visited by the child, apply filters to the categories of sites at risk (which will be immediately blocked), prevent the installation of dangerous apps and lock / unlock the device remotely, setting the precise times of use. This app is probably the best one to be able to control the activity of your child, since it offers effective filters, it is not possible to uninstall or stop it without the safety consent and password and also acts at the app level, allowing you to block pages too Websites that can be visited by other apps.
If instead we want to apply a DNS type filter on our Android smartphone or tablet, we can use the free DNS changer app.
With this app installed we can quickly apply any type of DNS server, choosing from those in the list or manually entering the protective DNS (for example those seen at the beginning of the guide and registered with OpenDNS), so as to prevent the opening of dangerous sites for minors. In addition to filtering via DNS, it also allows you to block a single site, simply adding the web address within the app settings.
Conclusions
All the methods we have shown you allow you to block a site from the router, PC and smartphone in a simple and effective way, especially if we have to protect the devices provided to children or minors. Many of the methods applied can still be overcome by children who are particularly good in computer science or able to search very well on Google, so we try to educate children in respecting the filters imposed and to navigate only on the sites we decide to unblock.Still on the topic we can read our two guides on Parental Control and family filter on PC and internet: 5 ways to keep children safe and How to protect children and family from the dangers of the Internet, which will give us an even wider overview of the methods that we can use to block one or more Internet sites.
