Instruction to make payment to prevent heartless child collection (4,5)
I believe the answer is:
bank draft
'instruction to make payment' is the definition.
(a bank draft is an order to make a bank payment)
'prevent heartless child collection' is the wordplay.
'prevent' becomes 'ban' (a ban is an attempt to prevent something).
'heartless' says to hollow out the word (remove centre letters).
'child' becomes 'kid' (synonyms).
'collection' becomes 'raft' (raft can mean a large collection of something).
'kid' with its middle taken out is 'kd'.
'ban'+'kd'+'raft'='BANK DRAFT'
'to' is the link.
(Other definitions for bank draft that I've seen before include "money transfer" , "Form of cheque" , "that is negotiable" , "order for payment" .)