The first group of juvenile detainees have been returned to the Banksia Hill detention centre after the facility was badly damaged in a riot.
One hundred and fifty detainees were moved to the adult Hakea Prison after the January riot.
The teenagers caused around $3-million damage which took months to repair.
The Department of Corrective Services says the cells have now been reinforced.
The Department hopes all of the juveniles will have been returned to Banksia Hill by the end of October.