i had the same issue with our eldest, she worked out my passwords and re enabled the access, then i changed the password and she worked out that if she reset the router it defaulted to orginal firmware and passwords helpfully written on the router - i was livid at this point as i have quite a big setup and takes me an age to get the network up and running again (i hate networks administration).
I then decided to change my router to a nighthawk and all was ok for a while until she worked out that she could bypass the nighthawk and re enable the router settings on the superdud (again default settings helpfully written on the router by virgin).
Ive now locked the modem in a cupboard - the nighthawk is out but she cannot reset that (and she has tried), she now has hacked a neighbours wifi to access (her tab and computer both will sign in).
So now i gained a new laptop and tab.....
I suppose what im saying is kids are so savvy now they will find a work around, mine did.
She has lost both machines now until she has learned its not acceptable, in the mean time im trying to find my neighbour that has password as thier wifi password!!.
Me and the wife found it hysterical the means she went to, i mean come on i dont remember ever having that much front...... i suppose it the same as sneeking out in the middle of the night to meet mates which i used to do very often.
Shes at this level now makes me wonder how good she will be at it when shes a adult.