Cheap number in English children's magazine (8)
I believe the answer is:
economic
'cheap' is the definition.
(I've seen this before)
'number in english children's magazine' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'in' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'children's magazine' becomes 'comic' (I've seen this before).
'e'+'comic'='ecomic'
'no' put into 'ecomic' is 'ECONOMIC'.
(Other definitions for economic that I've seen before include "Capable of operating at a profit" , "Inexpensive" , "Relating ot the management of wealth" , "Sparing in the use of resources" , "Fiscal" .)