Mixes cress into lamb! (9)
I believe the answer is:
offspring
'lamb' is the definition.
(thesaurus)
'mixes cress' is the wordplay.
'mixes' becomes 'off' (I can't justify this - if you can you should believe this answer much more).
'cress' becomes 'spring cress' (spring cress is a kind of cress).
'off'+'spring'='OFFSPRING'
'into' acts as a link.
Can you help me to learn more?
(Other definitions for offspring that I've seen before include "Kids" , "Young" , "Result" , "Issue for raising" , "Children, issue" .)