Kids can use a floppy one (4)
I believe the answer is:
disk
'use a floppy one' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'kids can' is the wordplay.
'can' indicates anagramming the letters (I've seen 'canned' mean this (canned can mean drunk)).
'kids' is an anagram of 'DISK'.
Can you help me to learn more?
(Other definitions for disk that I've seen before include "Thin, flat, circular plate" , "Floppy - - (comput.)" .)