What is the ruling on recording Islamic children's songs with a female singer's voice, then processing it to sound like a child's voice, and is it permissible to listen to or market these recordings?

This method cannot be judged except by knowing the mechanism by which it is executed, and who listens to the singers' voices and transforms them. It is not permissible for a man to listen to the singing of a non-mahram (definition) woman. If there is temptation or fear from these tapes or others, it is obligatory to prevent them, and not to listen to them or market them. If there is no such thing, then there is no objection to them.