Milling around thinking over swapping with adult (9)
I believe the answer is:
wandering
'milling around' is the definition.
(to mill around is to wander or travel aimlessly)
'thinking over swapping with adult' is the wordplay.
I cannot really understand how this works, but
'with' could be 'and' and 'and' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for wandering that I've seen before include "Rambling" , "Straying" , "Oceanic animal -- large bird's not a swan (anag)" , "vagrant" , "Moving about aimlessly" .)