Peg had a broken night - it made the baby cry (8)
I believe the answer is:
teething
'peg had a broken night it made the baby cry' is the definition.
I can't tell whether this defines the answer.
'peg had a broken night' is the wordplay.
'peg' becomes 'tee' (tee is a kind of peg).
'had' says to put letters next to each other.
'a broken' is an anagram indicator.
'night' with letters rearranged gives 'thing'.
'tee'+'thing'='TEETHING'
Can you help me to learn more?
(Other definitions for teething that I've seen before include "Painful time for baby" , "It'd painful for baby" , "- Troubles occur in the early stages of a project" , "problem in infancy" , "Occasion of initial troubles" .)