The following are the responses of the grand maraji':[1]

His eminence, Ayatullah Khamene'i (may Allah prolong his life):

In the case of the question, it is not permissible.

His eminence, Ayatullah Sistani (may Allah prolong his life):

It is not valid as per obligatory precaution, even if the leader is 10 years of age.

His eminence, Ayatullah Saafi Golpaygani (may Allah prolong his life):

The leader of prayers must be baligh.

Ayatullah Mahdi Hadavi Tehrani (may Allah extend his blessings):

In this case, one who has better recitation or at least, correct recitation and is more religious is more suitable to lead the prayer; in any case, jamaa'ah prayer is something good.