Nine-year-old Seena Aklashi Sheikhdost was one of 22 survivors from the asylum-seeker boat that broke apart off Christmas Island on December 15.
After the threat of court action by human rights lawyers, Seena was given permission to return to Sydney with his relatives.
The nine-year-old, eight of his relatives from the detention centre, and two other children orphaned in the boat tragedy, arrived in Sydney at 11pm (AEDT) on Thursday.
They were housed in two duplexes in Granville in western Sydney, Jamal Daoud of the Social Justice Network said.
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Mr Daoud told AAP the group were resting after their long journey from Christmas Island.
"My understanding is that only Seena has been given a permanent visa so far," he said.
Seena's Sydney-based cousin, Jaffar Al-Ghbar, said on Thursday that Seena would would first receive medical treatment and then attend a local school when he is ready.
Seena's father, Farhan, was buried at Rookwood Cemetery, in Sydney's west, last week.
His mother perished in the boat crash and her body has not been recovered.
