If you want to play a decisive role in a user's access to some or all sites on the internet, these two browser extensions (BlockSite - Stayfocusd ) will be with you in your decisive role.
For example, the only precaution that can be taken against the possibilities that your little brother may do on the internet is to deactivate all sites on the internet through the BlockSite extension, except for some whitelisted sites.
Also if you want to spend a certain amount of time on some of the whitelisted sites on a daily basis, you can add these sites as a group and determine their time via the StayFocusd extension.
Or did he/she turn out to be a genius? In this case, block the extension settings page.
Unbelievable! Or did he/she try to download and play the block breaking and putting game using USB or an external device? Try checking it out at StayFree. That was too commercial, even though I don't want it.