Delete files and folders recursively in subdirectories

There is a folder, "transfer". In that transfer folder there are user folders "user1", "user2", etc. I want to (periodically) delete the content (i.e. all files and folders in the user folders) but I do not want to delete the "transfer" or user folders. How can I do that using as shell script/command without manually adding a call for each new user folder every time I add a new user?