[This Convention does not apply to work done by children and young persons in schools for general, vocational or technical education or in other training institutions, or to work done by persons at least 14 years of age in undertakings, where such work is carried out in accordance with conditions prescribed by the competent authority, after consultation with the organizations of employers and workers concerned, where such exist, and is an integral part of:] a programme of training mainly or entirely in an undertaking, which programme has been approved by the competent authority; or