Viewing a login file

I would like to create a log file to log when a member of the server logs in to the server/joins or whatever you want to call it. This way I can know when and who logged in at what time. Since I am the administrator, manager, and owner of a server which has underage subscribers, I heavily moderate this server (CATS @ SCHOOL). I cannot find a log file which tells me who and when someone logs in to the server.

Thank you in advance for any information which will assist me in managing this server.