Hello Josh,

I have thought about it doing from process builder but there are lots of scenarios that I can think of which process builder wouldn't be able to take care but however, Let me offer you a trigger which would do the job. Giev it to your developer and he would modify it based on your objects and requirements a little but the real bulk is alredy WRITTEN!!
Parent Object: Contact
             Fields: Quantity__c
Child Object: Credit__c
             Fields: Contact__c (a lookup relation field to contact)

This is what the trigger does:
Whenever you create a Contact record and provide 5 (or any number) on Quantity__c field then trigger would create 5 (or any number) of records for associatd child object.
(e.g., if I create a contact record named Josh Tonks and provide nothing in Quantity__c field then it will not create any automatic child records.
If I provide 10 inside a Quantity__c field then it will automatically generate 10 Credit__c object record for this contact named Josh Tonk)

1) Let's put NULL or ZERO in Quantity__c field.
          
2) Now, let's enter 10 inside that Quantity__c field and see the magic of 10 child record creation automatically
   

Trigger Code:
 

Trigger CreatingAutoRecords on Contact(After Insert, After Update)
{
    
    List<Credit__c> creditRecordsFinalListToInsert = New List<Credit__c>();
    
    If(Trigger.IsInsert || Trigger.IsUpdate)
    {
        For(Contact con : Trigger.New)
        {
            If(con.Quantity__c != null)
            {
                List<Credit__c> fetchingAlreadyExixtsedRecords = [Select Id FROM Credit__c WHERE Contact__c =:con.Id];
                
                If(fetchingAlreadyExixtsedRecords.IsEmpty())
                {
                    // We are only creating a records when there is no Credit__c records exixts.
                    For(Integer I = 0; I < con.Quantity__c; I++)
                    {
                        Credit__c crd = New Credit__c();
                        
                        crd.contact__c = con.Id;
                        crd.Name       = 'Sample Name' + I;
                        creditRecordsFinalListToInsert.add(crd);
                    }
                }
                
            }
            
            try{
                If(!creditRecordsFinalListToInsert.IsEmpty()){
                    insert creditRecordsFinalListToInsert;
                }
            }
            Catch(Exception e){
                System.debug('The thrown exception for CreatingAutoRecords is:: ' + e.getMessage());
            }
        }
    }
    
    
}

You or your developer person can definitely modify the trigger in a way which works best for your org requirements. But as far as the auto creation goes, it has been taken cared by trigger.

Hope this helps and if it answers your question then please mark it as best answer since it will help other users in community with the similar query!