parental control app for open-source desktop

Aside from politics and digital-id whatever its called, is there any
real good working "parental control" solution for the open-source
platforms for parents that want to give ~10yo kids their first
computer?

Something that would block nasty sites, monitor activity, set timers,
math riddles to the (un)lock screen, etc.

There are solutions for mobile platforms and commercial desktop OS but
is there anything for BSD/Linux desktops?

We could convince parents to use open-source desktops with some safety
mechanisms provided on the older computers usually available for free
:-)

Maybe even a dedicated use-case for FreeBSD installer :-)

Any hints appreciated :-)

--
CeDeROM, SQ7MHZ, http://www.tomek.cedro.info