Jennifer Hudson and David Otunga cannot use their son's child therapist to make their custody case ... at least that's what the lawyer for the 8-year-old is demanding ... TMZ has learned.
The lawyer the judge appointed to represent David Jr. has filed legal docs asking the judge to prohibit Jennifer or David from calling the therapist to the stand to testify about the boy's state of mind and how the custody war has affected him.
We're told the reason the lawyer wants the protective order is so David Jr.