Home schooling to start — little ones very amused (2,8)
I believe the answer is:
'very amused' is the definition.
(in stitches can mean laughing uncontrollably)
'home schooling to start little ones' is the wordplay.
'home' becomes 'in' ('he's home' can mean 'he's in').
'to start' says to take the initial letters.
'little ones' becomes 'titches' (titch can informally mean a small person).
The initial letter of 'schooling' is 's'.
(Other definitions for in stitches that I've seen before include "you may be laughing" , "Laughing a lot" , "as one may be on leaving the theatre?" , "extremely amused" , "After an operation" .)