Twin boys first to assess forage crop (7)
I believe the answer is:
alfalfa
'forage crop' is the definition.
(I've seen this in another clue)
'twin boys first to assess' is the wordplay.
'twin' indicates the doubling of some letters.
'boys' becomes 'alf' (I can't justify this - if you can you should give a lot more credence to this answer).
'first to' suggests taking the first letters.
The first letter of 'assess' is 'a'.
'alf' duplicated is 'alfalf'.
'alfalf'+'a'='ALFALFA'
Can you help me to learn more?
(Other definitions for alfalfa that I've seen before include "odder plant" , "Lucerne, a fodder plant" , "A forage plant" , "Plant used as fodder" , "cattle feed" .)