[idi banashapan]

first port of call is to have a proper sit down with your children and talk to them about acceptable use. treat the computer use as a trust exercise and sell it as that. do not chair the talk as though you are telling them off either - talk to them in a manner akin to the level of maturity you wish them to act at. if they prove they can be trusted, reward them. don't go straight into punishing them by blocking their access - this will only serve as a catalyst into defying you or actively seeking out ways in which to circumvent your efforts to stop them doing whatever.

if you still find you get yourself to a point where you need to assert an authoritative stamp on the situation, buy a cheap router and set it up for wifi for the kids using a separate SSID and password. change the password on your normal wifi and do not tell them what it is. give them access to the new router. then at night, unplug it and put it in your room. job done. they will have no wifi they can connect to.