(1) A child shall be a qualified child (in this Part referred to as "a qualified child") for the purposes of child benefit if -
(a) he is under the age of 16 years, or
(b) having attained the age of 16 years he is under the age of 18 years and -
(i) is receiving full-time education, the circumstances of which shall be specified in regulations, or
(ii) is, by reason of physical or mental infirmity, incapable of self-support and likely to remain so incapable for a prolonged period, and
(c) he is ordinarily resident in the State, and
(d) he is not detained in a reformatory or an industrial school and is not undergoing imprisonment or detention in legal custody.
(2) Notwithstanding subsection (1), a child who resides with a qualified person while such person (being a member of the Defence Forces or the civil service of the Government or the State) is in the service, outside the State, of the Government, the State or an international organisation, shall be a qualified child for the pur