It is said to be coming from young child (4,4)
I believe the answer is:
baby talk
'it is said to be coming from young child' is the definition.
The definition suggests a singular noun which matches the answer. I also know that 'young child' relates to this answer.
'young child' is the wordplay.
'young' becomes 'baby' (similar in meaning).
'child' becomes 'talk' (I can't justify this - if you can you should give a lot more credence to this answer).
'baby'+'talk'='BABY-TALK'
Can you help me to learn more?
(Other definitions for baby talk that I've seen before include "Childish language" , "Childish prattle" , "Goo-gooing and gaa-gaaing" .)