Utilising them is child's-play, of course (4)
I believe the answer is:
toys
'utilising them is child's-play of course' is the definition.
I can't judge whether this definition defines the answer.
'play of course' is the wordplay.
'play' becomes 'toy' (synonyms).
'of course' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'toy'+'s'='TOYS'
Can you help me to learn more?
(Other definitions for toys that I've seen before include "Things that provide amusement" , "Trifles with playthings" , "Children's playthings" , "Small dogs" , "Film" .)