Main plant producing wonder in children (7)
I believe the answer is:
seaweed
'main plant' is the definition.
(I've seen this before)
'wonder in children' is the wordplay.
'wonder' becomes 'awe' (awe is a kind of wonder).
'in' indicates putting letters inside.
'children' becomes 'seed' (I've seen this in other clues).
'awe' put within 'seed' is 'SEAWEED'.
'producing' acts as a link.
(Other definitions for seaweed that I've seen before include "Plant such as kelp" , "Main plant" , "Coastal plants" , "Wrack" , "Marine plant" .)