My immediate thought is the following: How would we react if there was a spontaneous Muslim prayer meeting and several children "converted?" On the other hand, we know that God will save his children - some through family, some through church family, some through evangelism, some through radio broadcasts, some through books, and some even through visions. Yes, he will bring some to himself through public school, which is wonderful.
It seems this was a spontaneous thing, which is great. If it was organized and/or supported by the authorities, then beware - because, one day, the shoe may be on the other foot.
And I do agree with others about not missing class. Again, how would we react to children of other faiths missing class because of prayer events?