To you, initially, it's not the real thing (3)
I believe the answer is:
'not the real thing' is the definition.
I can't judge whether this defines the answer.
'to you initially' is the wordplay.
'initially' suggests taking the first letters.
The first letter of 'you' is 'y'.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for toy that I've seen before include "Teddy or Dolly" , "A child's plaything" , "Doll or teddy, say" , "Object for a child to play with" , "Small breed" .)