Little Rod is young creature (7)
I believe the answer is:
tadpole
'young creature' is the definition.
'tadpole' can be an answer for 'creature' (tadpole is a kind of creature). I am not certain of the 'young' bit.
'little rod' is the wordplay.
'little' becomes 'tad'.
'rod' becomes 'pole' (synonyms).
'tad'+'pole'='TADPOLE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for tadpole that I've seen before include "Immature amphibian" , "Young amphibian" , "developed from spawn" , "Aquatic larva of frog or toad" , "To plead for tiny frog" .)