MySQL ERROR - # 1452 - Can not add or update a child row

I have the following tables:

CREATE TABLE IF NOT EXISTS 'vagas' (
  'id' int(10) unsigned NOT NULL AUTO_INCREMENT,
  'empresa' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'funcao' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'qnt_vagas' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'carga_horaria' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'salario' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'email' varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  'telefone' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'estado' int(10) unsigned NOT NULL,
  'cidade' int(10) unsigned NOT NULL,
  PRIMARY KEY ('id'),
  KEY 'estado' ('estado'),
  KEY 'cidade' ('cidade')
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=5;

CREATE TABLE IF NOT EXISTS 'cidades' (
  'id' int(10) unsigned NOT NULL AUTO_INCREMENT,
  'nome' varchar(255) COLLATE utf8_unicode_ci NOT NULL,
  'estado' int(11) NOT NULL,
  PRIMARY KEY ('id')
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=2;

CREATE TABLE IF NOT EXISTS 'estados' (
  'id' int(10) unsigned NOT NULL AUTO_INCREMENT
  'nome' varchar(3) COLLATE utf8_unicode_ci NOT NULL,
  PRIMARY KEY ('id')
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=3;

All have records included, the problem that came up a change for me to do, in the case I have to put the state and city fields. I used this command:

ALTER TABLE 'vagas' ADD  CONSTRAINT 'vagas_fkcidade' FOREIGN KEY ('cidade') REFERENCES 'cidades'('id') ON DELETE NO ACTION ON UPDATE CASCADE;

But the following error occurs:

  

# 1452 - Can not add or update child row: a foreign key constraint fails ( #sql-de8_d8 , CONSTRAINT vagas_fkcidade FOREIGN KEY   ( cidade ) REFERENCES cidades ( id ) ON DELETE NO ACTION ON UPDATE   CASCADE)

I need to include these fields in the table.