hello friends
here i have write a trigger that copy data from parent obj to child when name is match
but in my trigger the following error shows (Didn't understand relationship 'Subscriptions__r' in FROM part of query call. If you are attempting to use a custom relationship, be sure to append the '__r' after the custom relationship name. Please reference your WSDL or the describe call for the appropriate names.) i dont undestand the problem
so plese help me 
here is my trigger 

trigger copyproductnametoaccount on Subscription__c (after insert,after update) //You want it on update too, right?
{
  Map<ID, Account> parentpname = new Map<ID, Account>(); //Making it a map instead of list for easier lookup
  List<Id> listIds = new List<Id>();

  for (Subscription__c childObj : Trigger.new)
  {
    listIds.add(childObj.membership_type__c);
  }

  //Populate the map. Also make sure you select the field you want to update, Rollno
  //The child relationship is more likely called Classes__r (not Class__r) but check
  //You only need to select the child classes a if you are going to do something for example checking whether the Classes in the trigger is the latest
  parentpname = new Map<Id, Account>([SELECT id, Product_Name__c,(SELECT ID, membership_type__c FROM Subscriptions__r) FROM Account WHERE ID IN :listIds]);

  for (Subscription__c sub : Trigger.new)
  {
     Account myParentpname = parentpname.get(sub.membership_type__c);
     myParentpname.Product_Name__c = Decimal.valueOf(sub.membership_type__c);
  }
    
  update parentpname.values();
}