Kids have an instinct for trouble... they'd find him even if he wasn't going to sing/pray. Speaking of which... what would a tone-deaf Finnish mage do? Hope the gods don't care if their ears hurt, or would he have to try and, uh, convert/switch to a different magic system that doesn't involve singing?

Maybe Minna put the kids in to make sure Onni wouldn't be too much of a Deus ex machina XD if every problem could be solved by Onni, there wouldn't be much fun.