Kid's playroom having railway laid down by nanny (7)
I believe the answer is:
nursery
'kid's playroom' is the definition.
'nursery' can be an answer for 'playroom' (I've seen this before). I'm unsure of the 'kid's' bit.
'railway laid down by nanny' is the wordplay.
'railway' becomes 'r' (eg in Great Western Railway).
'laid down' becomes 'y' (I can't explain this - if you can you should give a lot more credence to this answer).
'by' means one lot of letters go next to another.
'nanny' becomes 'nurse' ('nurse' can be a synonym of 'nanny').
'r'+'y'='ry'
'ry' after 'nurse' is 'NURSERY'.
'having' acts as a link.
Can you help me to learn more?
(Other definitions for nursery that I've seen before include "Baby's room - plant centre" , "Room for baby or baby plant" , "Kids' playroom" , "Place for tending young children, or plants" , "Place for cuttings" .)