Little kid’s first few days (4)
I believe the answer is:
week
'few days' is the definition.
(a week is 7 days)
'little kid's first' is the wordplay.
'little' becomes 'wee' (similar in meaning).
'kid's first' becomes 'k' (1st letter of 'kid').
'wee'+'k'='WEEK'
(Other definitions for week that I've seen before include "Part of the year" , "Seven days" , "Seven day period" , "A long time in politics?" , "Calendar period" .)