Drama writer barred for the very young (7)
I believe the answer is:
'barred for the very young' is the definition.
I can't judge whether this definition defines the answer.
'drama writer' is the wordplay.
'drama' becomes 'play' (synonyms).
'writer' becomes 'pen' (something which writes).
Can you help me to learn more?
(Other definitions for playpen that I've seen before include "Portable enclosure for tots" , "Child's enclosure" , "Enclosure for child" , "juvenile restraint" , "device to capture the young" .)