ANGELINA JOLIE is fighting to keep her family together after the birth mother of her adopted son PAX begged to reconcile with him!

The Vietnamese-born 8-year-old’s heroin-addicted mom has kicked her drug habit and desperately wants to reconnect with him, sources say. But Angelina believes a reunion would be too overwhelming for Pax right now.

“Angelina is going through every adop­tive mother’s worst nightmare,” said an insider.

“She’s stonewalling Pax’s birth mom because she thinks Pax is too young and  impressionable to understand the complexities of his biological mother’s life.

“But Angie is also deeply insecure and worries Pax could become so confused that he’ll want to return to his mom. She’s also wonder­ing if Pax’s mother is making a play to reclaim him.”

The Oscar-winner, 36, and partner Brad Pitt ad­opted Pax from a Vietnamese orphanage in March 2007 when he was just 3 years old.

His biological mother Pham Thu Dung had been a drug addict since the age of 16, and she abandoned Pax in the hospital two days after giving birth in Novem­ber 2003.

Her parents also signed papers releasing Pax for adop­tion, but as The ENQUIRER reported, Dung once vowed: “My dream is that one day he will come back to visit me and call me mother.”

Now clean of drugs, 34-year-old Dung has reached out to the adoption agency that placed Pax with the superstar couple and asked that she be reunited with her son.

“Angie nearly keeled over when she found out that Dung wants her to bring Pax to Vietnam to meet his biological family,” said the source.

“She wailed to Brad, ‘Don’t let them take away my boy!’ But once she pulled herself together and re-evaluated the situation, Angie agreed that Pax should be rein­troduced to his birth mother – just NOT right now.

“She doesn’t want to disrupt the stability she and Brad have worked so hard to provide. Angie also thinks Pax is too young to be exposed to the harsh realities surrounding his birth and adoption.”