For most events in the conference center you need to be 8 or older. This is largely because the events are televised and children need to be mature enough to be quiet throughout the entire meeting. Sounds of crying, whining, even rustling papers and candy wrappers in the audience can be picked up on the recording.
Similar to the priesthood sessions, where you had to be 12 and above, the sisters need to be 8 and above.
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