List<Contact> con = [SELECT Id, (SELECT Id, Name, CreatedDate, ContentType FROM Attachments WHERE ContentType ='application/pdf' ORDER BY CreatedDate DESC) FROM Contact LIMIT 10];

for (Attachment a : con.Attachments) {
  if (a.Name.startsWithIgnoreCase('Resume_')) {
    [...]
  }
}

Contact[] people = [SELECT (SELECT Name FROM MothersChildren__r),
                           (SELECT Name FROM FathersChildren__r)
                    FROM Contact];

for (ChildRelationship relation : SObjectType.Contact.getChildRelationships())
    if (relation.getChildSObject() == Attachment.sObjectType)
        system.debug(relation.getRelationshipName());

SELECT Name, (SELECT Name FROM Job_Applications__r) FROM Position__c