California Code of Civil Procedure Section 2017.010 states that any party may obtain discovery regarding any matter that is relevant to the subject matter of the legal action, if the matter is itself admissible as evidence or will with reasonable belief lead to the discovery of admissible evidence. In other words, any information that is relevant to the child custody case (and not privileged) can be “discovered” as evidence to support the case during the discovery phase.
California Evidence Code Section 940, however, prevents self-incriminating information from discovery in a family law case. This law states that an individual has the privilege to refuse to disclose any information that may incriminate himself or herself. If a child custody case involves allegations of domestic violence, for example, the spouse who is facing the allegations legally does not have to answer any questions about the incident if the answers will tend toward self-incrimination.