Halle Berry and Olivier Martinez refused to hold court with reporters on their way into court amid their nasty custody battle ... letting their 13-year-old son do all the talking ... under seal.

Halle was seen walking down the courthouse steps in a dark pantsuit and sunglasses, surrounded by cameras as she made her entry bright and early Monday ... but she was in no mood to answer questions.

TMZ also caught Olivier heading back into court after a lunch break in downtown Los Angeles ... but he wasn't in the mood to talk, keeping his mouth shut as he ducked back inside.

Their 13-year-old son, Maceo, testified during the hearing -- which is still ongoing -- with the judge ordering both parents out of the courtroom while he spoke. His testimony is under seal.

We're told Halle arrived first, followed by Olivier and Maceo together ... and things got icy when Halle glared at her ex as he entered the courtroom.

As TMZ first reported, Olivier accused Halle of attacking and choking Maceo during an argument over a virtual reality video game -- allegations she's strongly denied.

A judge previously granted Olivier a temporary restraining order limiting Halle's contact with their son. Olivier is seeking sole custody, while Halle wants their previous shared custody arrangement restored.