It's ill-judged to train entire CID guarding son (10)
I believe the answer is:
indiscreet
'it's ill-judged' is the definition.
(I've seen this before)
'train entire cid guarding son' is the wordplay.
'train' indicates anagramming the letters (to train can mean to grow something into a shape).
'guarding' means one lot of letters goes inside another.
'son' becomes 's' (genealogical abbreviation for son).
'entire'+'cid'='entirecid'
'entirecid' anagrammed gives 'indicreet'.
'indicreet' going around 's' is 'INDISCREET'.
'to' acts as a link.
(Other definitions for indiscreet that I've seen before include "Too ready to tell secrets" , "Tactless" , "Imprudent -- 10 across (anag)" , "Reckless" , "Too ready to reveal secret things" .)