Youngster at home with fellow worker (6)
I believe the answer is:
infant
'youngster' is the definition.
(I've seen this before)
'home with fellow worker' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'with' says to put letters next to each other.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'worker' becomes 'ant' (worker is a type of ant).
'in'+'f'+'ant'='INFANT'
'at' is the link.
(Other definitions for infant that I've seen before include "Very young child or baby" , "Very small child" , "Tot" , "Youngster" , "Small baby" .)