How difficult it is has a lot of variance. Unifi make it easy to get up and going for example.

Unifi Network, make network, content filtering: family, save. Make WiFi, assign to network, save. Then you can just never give you kids access to the default network. Or you can blacklist their devices. If you want to get more advanced firewall rules are fairly easy to add as well.

IIRC a trick you can do is take a heat gun (or failing that a hair dryer) and warm up the magnet gasket border thing. Then close the door and leave it for a bit. Something about it better forming to the correct shape and making a better and more consistent seal.

Couldn’t hurt!