Hiring/Renting: Hiring a Minor Who Does Not Have a Guardian
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 2186
It is not allowed to give on hire a minor (ṣaghīr) who does not have a guardian without authorisation from a jurist (mujtahid).[1] As for someone who does not have access to a jurist, he can obtain authorisation from a dutiful (ʿādil) believer and give the child on hire.
-Ayatullah Sistani, Practical Laws of Islam, Hiring/Renting (Ijarah)
1
Ruling 2091 provides further clarification of this term: it refers to someone who spends his wealth in futile ways.