Unduly optimistic son to stay and watch daughter (6-4)
I believe the answer is:
starry-eyed
'unduly optimistic' is the definition.
'starry-eyed' can be an answer for 'optimistic' ('starry-eyed' can be similar in meaning to 'optimistic'). I am not sure about the 'unduly' bit.
'son to stay and watch daughter' is the subsidiary indication.
'son' becomes 's'.
'to stay' becomes 'tarry' (I can't justify this - if you can you should believe this answer much more).
'and' is a charade indicator (letters next to each other).
'watch' becomes 'eye' (I've seen this before).
'daughter' becomes 'd'.
's'+'tarry'+'eye'+'d'='starryeyed'
Can you help me to learn more?
(Other definitions for starry-eyed that I've seen before include "Out of touch with reality" , "Full of unsophisticated optimism" , "Naively enthusiastic" , "Romantically optimistic" , "Naively idealistic" .)