u can start with wireshark that is easiest. then look into other ways like ettercap , cain& able and so on
OP wants to do it on a remote network.
And with 'got into bla bla' he means he found some default logins.
He can login to the GUI or maybe a telnet session but thats about it.
Not so sure if we should help the kid.
If he is talking about wireless routers he cracked for whatever reason then yes wireshark seems like a reasonable option.
Then again,not so sure if we should help the kid.