prevent parent record deletion

what I want to know is if a List object is present inside a loop will it hit governor limits?

public class preventaccountdeletion
{
   public void prevent_account_delete(list<Account> acc)
   {
       for(Account a:acc)
       {
          List<Contact> con=[select AccountID from Contact where AccountID=:a.ID];
          List<Opportunity> op=[select AccountID from Opportunity where AccountID=:a.ID];
          if ((con.size() > 0) || (op.size() > 0))
             a.addError('Cannot Delete Account Because It Has Related Contacts And Opportunities');
       }
   }
}
trigger trg_preventaccountdelete on Account (before delete)
{
   if (trigger.isDelete)
   {
     preventaccountdeletion p=new preventaccountdeletion();
     p.prevent_account_delete(Trigger.old);
   }
}