Streisand said the weapon was ordered by the 13-year-old son of Jermaine Jackson, Jafar, and sent to the Jackson family home in the Encino neighborhood of Los Angeles. Jermaine Jackson's children also live in the home.
"Jafar opened the package in his bathroom and tested it on a piece of paper," Streisand said in a statement. He said security and Katherine Jackson heard the sound and confiscated the weapon immediately.
He said Michael Jackson's oldest son, Prince, saw the stun gun after it was taken by security.
"Blanket Jackson never saw or heard the Taser," Streisand said in the statement. "Neither did Paris Jackson. Prince saw the Taser in possession of security."
Streisand said child services workers have not provided him or Katherine Jackson with an update on the agency's inquiry. A phone message left for the agency was not immediately returned, but it doesn't usually comment on its cases.
"All of the kids are happy, healthy and wonderful, and that is Mrs. Jackson's only objective and concern," Streisand said.
Katherine Jackson has been caring for the children since their father's death June 25 at age 50. The children range in age from 8 to 13.
All attended a star-studded memorial held in July at the Staple Center. The eldest children, Prince Michael and Paris, also spoke during a segment at February's Grammy Awards where Michael Jackson was given a posthumous lifetime achievement award.
Their father was fiercely protective of his children's privacy and images, often covering their faces when they were in public.
Prince Michael and Paris are the children of Michael Jackson's ex-wife Debbie Rowe, who was granted some visitation with them after the singer's death. The identity of Blanket's mother has never been revealed.
As part of an agreement between Rowe and Katherine Jackson, a child psychologist was required to structure visits and monitor the children. Katherine Jackson was initially granted more than $86,000 a month to pay for the family home and care for Michael Jackson's children, but that allowance was recently increased. The current amount has not been publicly disclosed.
A Los Angeles Superior Court judge has oversight of Katherine Jackson's guardianship of the children and has praised her in open court.
Streisand said in an e-mail that he does not expect the stun gun incident to become a factor in the guardianship case. Meg Lodise, a court-appointed attorney representing the three youngsters' interests in their father's estate, did not return a phone message seeking comment.