I have kids sharing. My older boys will settle quickly when I tell them they will loose computer privileges the next day if they don't settle.
The younger kids.. My 4 & half yr old has a light & I tell him I will have to take it away if he doesn't settle down, be quiet & go to sleep.
I might sound mean but I have resorted to threats of taking things away. It works & I have never had to take away his light.

You might find some visuals will work also. Print out little picture of what is expected of them once in bed (A child sleeping in bed) and maybe a picture of it being night time & one of reading a bed time story & one of saying good night. Put them all in order & show them, it is time for sleeping now.

Give them 1 warning & if it continues then out goes the night light!