Judge Mitchell Beckloff ordered the inquiry after Paris Jackson was hospitalised on June 5 for taking Motrin pills and cutting her arm with a kitchen knife.
Beckloff ordered an investigator to interview Jackson's children, including Prince and Blanket, and report back to him.
Beckloff said he also met with attorneys for the children's grandmother Katherine Jackson and their adult cousin TJ Jackson, who serve as guardians.
"I'm taking no further action," Beckloff told attorneys for the Jackson estate during a hearing on an unrelated matter.
Sanders and Charles Shultz, an attorney for TJ Jackson, have said the judge's inquiry was an expected move and they supported his decision.