Beg your pardon? Werewolf cubs. If anything, this'd have to be a figure of speech.
I'm sure 'keeping' a flock of small children under your bed isn't all that conspicuous. It's a school, there are kids around every corner. They might just be a wee little bit small for their age and very... shy. And around full moon they could be locked into the trunk :D

'It was a name I was already using at Hogwarts, to my most intimate friends only, of course[...]'
maybe they really did call him Voldie. If one of my friends wanted to be called Lord Voldemort (or something similar demented for a perfectly ordinary teenager) I'd call them Voldie or Voldiepoo just to make them snap out of it.