It's been updated in the wiki!
btw, the last 42rc (rc9) refers to it as /ip kid-control.
to be honest, identifying devices by their IP address is kind of dumb. especially since dual stack is not a thing and most of our kid's devices support seamlessly IPv6. i learned it on a hard way - got my fine-tuned parental control stuff running ~2yrs ago and next day they were still watching youtube videos instead of doing their homework. iOS just uses whatever it is available, so the videos fell back to IPv6 as the browser realised the v4 content is accessible no more, without any user intervention.
and since all the devices implement IPv6 privacy extensions, a simple v6 capable terminal can have multiple v6 addresses simultaneously.
so my approach is based on mac address: i set up a mangle rule both for v4 and v6, where i assign all the device's mac addresses to a marked connection, then in _both_ firewalls (v4/v6) i can easily match on the flow and apply the necessary enforcement.
6 chain=prerouting action=mark-connection new-connection-mark=kid1
7 chain=prerouting action=mark-connection new-connection-mark= kid1
8 chain=prerouting action=mark-connection new-connection-mark= kid2
9 chain=prerouting action=mark-connection new-connection-mark= kid2
then scheduled events can enable & disable the respective firewall rules based on their "comment" value using regex matching.
i hope the kid-control will also utilise mac addresses soon.