All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
In principle, a Muslim is innocent from all accusations and one should think good of him until the contrary is proven. Allaah Says (what means): {O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin.}[Quran 49:12] Moreover, Abu Hurayrah narrated that the Prophet said: “Beware of suspicion, for suspicion is the worst of false tales.” [Al-Bukhari and Muslim]
Therefore, it is not permissible to accuse this Imaam just because of the statement of those boys especially that he is an Imaam of the mosque, as this accusation is very serious and it may lead to thinking bad of the people who are supposed to be a good example for other Muslims.
Therefore, it is an obligation to warn those boys against spreading such accusations and not to take them into account.
Allaah Knows best.