I imagine them downloading movies and images that get me into trouble with the wife / LEAs / both.
I'm Dick with the FBI. Is your husband home?
I will get in trouble with my wife because the feds will rat me out to her for something stupid these hypothetical kids end up doing.
Usually it's meth heads trying to steal something that is easy to grab not the CIA.
Chrome lets me add an exception for the box itself, but really how many end user do you know that will not click on "take me to the http version(unsafe)", when talking about their home router?
So given the fact that I am in your wifi, One could use dhcp (if active) for MITM attacks, grab the router password and install tracking daemons right on top.
Next step would be to forward the dns requests to one of mine so I can build a map of what sites you use and from there all I have to to is to make you accept an insecure ssl cert and done?