I have installed a Disney 'Circle' device - its like a really handy device that allows you to control web/internet conrols on a device by device level - so in this case, you set the child's device as locked down - and can add/delete whitelist/blacklists or use the built in profiles. They can be found cheap on ebay.
Also means they are tamper proof (i.e. kids looking for workarounds on the device) and you can manage remotely... also good for blocking app stores, xxx content and individual sites that you want kids away from.
For me - this (or a similar device) is the way to go, vs local software.
Best,
Kev