Legal Question in Family Law in California

Sorry. But what even makes you even think you can just bring the mediator in as a witness? I'm not going into legalities with a layman so I'll say it this way. It is called mandatory and private mediation for a reason. if people knew the mediator would testify it would thwart mediation and settling cases. According the law, specially the Evidence Code is written to keep the mediator from testifying with few exceptions.

Consult a local attorney about the mediator testifying to go over what you're trying to do and seek court permission to have a child witness.