Women's Aid initially provided for homeless child (4)
I believe the answer is:
Here is my best explanation:
'homeless child' is the definition.
(I've seen this before)
'women's aid initially provided' is the subsidiary indication.
'initially' suggests taking the first letters.
'provided' becomes 'if'.
The initial letters of 'womens aid' is 'wa'.
'for' is the link.
(Other definitions for waif that I've seen before include "Homeless child - thin person", "Ragamuffin", "Very thin person", "orphan", "Abandoned child", "Neglected, homeless child", "Foundling", "neglected issue", "Orphan" and "Gamin".)