This should be enabled by default on all new connections.
That solution is not fool proof and is easily bypassed by using alternative DNS settings on a device. For a more robust solution I'd suggest looking at the settings on the devices you use for options to block adult content, or invest in a third party router and put the hub in modem mode.
A quick Google search brings up these lists of best parental control routers:
PS if you use virigin Hub in modem mode, with your own router, you have more control, more options. you can password protect access to the DNS setting on your own router. the bypass is then to use mobile data [ which every teenager knows ]