What is the ruling on naming the opening ceremony of a da'wah camp an "operetta," and on establishing a large prayer hall next to it to gather people behind a reciter with a beautiful voice and deliver speeches after the prayer, with the intention of attracting them to attend the events?

An operetta is a type of musical play, and this term should not be applied to an opening ceremony for recreational and da‘wah activities. There is no harm in establishing a prayer area (musalla) next to the caravan's camp where speeches can be delivered after prayers, with care taken to manage the young children.