code: private static Map<Long, ManagedCustomer> getAllManagedCustomers(
        AdWordsServicesInterface adWordsServices, ImmutableAdWordsSession session)
        throws RemoteException {
      // Get the ManagedCustomerService.
      ManagedCustomerServiceInterface managedCustomerService =
          adWordsServices.get(session, ManagedCustomerServiceInterface.class);
  
      SelectorBuilder selectorBuilder =
          new SelectorBuilder()
              .fields(ManagedCustomerField.CustomerId)
              .equals(ManagedCustomerField.CanManageClients, "false")
              .limit(PAGE_SIZE)
              .offset(0);
  
      ManagedCustomerPage managedCustomerPage;
      int offset = 0;
      Map<Long, ManagedCustomer> managedCustomers = Maps.newHashMap();
      do {
        selectorBuilder.offset(offset);
        managedCustomerPage = managedCustomerService.get(selectorBuilder.build());
        if (managedCustomerPage.getEntries() != null) {
          for (ManagedCustomer managedCustomer : managedCustomerPage.getEntries()) {
            managedCustomers.put(managedCustomer.getCustomerId(), managedCustomer);
          }
        }
        offset += PAGE_SIZE;
      } while (offset < managedCustomerPage.getTotalNumEntries());
  
      return managedCustomers;
    }
docs: Retrieves all managed customers under the manager account identified by
  {@link AdWordsSession#getClientCustomerId()}.