Parental Controls
In Linux Mint, you can limit your child's ability to make changes to the computer or download software. This can be set up simply by managing the administrative access settings of your child's account.
Limit Web Browsing
Google Chrome: Instructions for parental controls (Family Link)
Mozilla Firefox: Instructions for setting up website blocking
For additional support, check out Nanny - a repository that can be added and installed through the Command Line.