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Zimbabwe
Practice Relating to Rule 137. Participation of Child Soldiers in Hostilities
Zimbabwe’s Constitution (2013) states:
Chapter 4 – Declaration of Rights
81. Rights of children
(1) Every child, that is to say every boy and girl under the age of eighteen years, has the right –
(g) not to be recruited into a militia force or to take part in armed conflict or hostilities;
86. Limitation of rights and freedoms
(2) The fundamental rights and freedoms set out in this Chapter may be limited only in terms of a law of general application and to the extent that the limitation is fair, reasonable, necessary and justifiable in a democratic society based on openness, justice, human dignity, equality and freedom, taking into account all relevant factors, including –
(b) the purpose of the limitation, in particular whether it is necessary in the interests of defence, public safety, public order, public morality, public health, regional or town planning or the general public interest;
(3) No law may limit the following rights enshrined in this Chapter, and no person may violate them –
87. Limitations during public emergency
(1) In addition to the limitations permitted by section 86, the fundamental rights and freedoms set out in this Chapter may be further limited by a written law providing for measures to deal with situations arising during a period of public emergency, but only to the extent permitted by this section and the Second Schedule.
(4) No law that provides for a declaration of a state of emergency, and no legislative or other measure taken in consequence of such a declaration may –
(a) indemnify, or permit or authorise an indemnity for, the State or any institution or agency of the government at any level, or any other person, in respect of any unlawful act; or
(b) limit any of the rights referred to in section 86(3), or authorise or permit any of those rights to be violated. 
Zimbabwe, Constitution, 2013, Sections 81(1)(g), 86(2)(b) and (3), and 87(1) and (4).
In 2013, in its second periodic report to the Committee on the Rights of the Child, Zimbabwe stated:
In terms of the National Service Act … persons can volunteer to join the army only at the age of 18 years. Where an emergency arises, the law obliges the government to recruit persons of 18 years and above for national service. The minimum age of participation in hostilities is therefore 18 years. 
Zimbabwe, Second periodic report to the Committee on the Rights of the Child, 13 April 2015, UN Doc. CRC/C/ZWE/2, submitted 27 May 2013, § 374.