The Los Angeles Department of Children and Family Services launched the probe as they discovered the extent of the singer's addiction to prescription drugs.

The investigators gently interrogated Prince Michael, 12, Paris, 11, and seven-year-old Prince Michael II - known as Blanket - to find out whether they were exposed to narcotics like methadone, the heroin substitute discovered from Jacko’s house.

According to an insider, social workers could take legal action themselves to safeguard the youngsters.

The investigators also questioned the kids about the ‘Thriller’ hitmaker’s behaviour towards them and their grandmother Katherine, 79 at her home in Encino, California.

“The investigation was initially launched because drugs are so heavily involved,” the Sun quoted an insider as saying.

"But in this particular case there are also red flags from all the family history and from Michael's prior involvement in molestation cases.

"The DCFS has 27 days to investigate the case and close it.

"They will check everyone involved in the children's lives for a criminal background.

"If they are satisfied the kids have been raised in a decent environment, then no further action will be taken.