Hallo ad4m
Have you seen this previous post (https://ubuntu-mate.community/t/nanny-parental-control-for-ubuntu-mate-a-fork-perhaps/1777)?
@Wimpy Hallo Wimpy, you said then that you’d be glad if someone would work on this, if I understand ad4m correctly they’re offering just that. Have you been in contact with each other?
If this results in a port of Nanny for Ubuntu-Mate I would suggest that it should be included in the software boutique.
Unfortunately I can’t code, so I can’t help directly.