One small child adopts a zoologist's last parrot (7)
I believe the answer is:
imitate
'parrot' is the definition.
(to parrot is to copy or imitate)
'one small child adopts a zoologist's last' is the wordplay.
'one' becomes 'i' (Roman numeral).
'small child' becomes 'mite' (informal term).
'adopts' indicates putting letters inside.
'last' indicates one should take the final letters.
The final letter of 'zoologist' is 't'.
'a'+'t'='at'
'mite' enclosing 'at' is 'mitate'.
'i'+'mitate'='IMITATE'
(Other definitions for imitate that I've seen before include "Copy (mannerisms)" , "Parrot" , "Mimic or follow as a model" , "Mock" , "I tame it (anag)" .)