The Perth parents who gave their three children excessive doses of powerful and addictive pain medications over almost a decade have been handed jail terms.

The couple, who cannot be named to protect the identity of their children, had each admitted three offences of "engaging in conduct that was reckless and may have resulted in the children suffering".

The offences were committed over eight years after the two boys and a girl were diagnosed with a syndrome called "Ehlers-Danlos", which affected the connective tissues in their bodies.

The District Court was told the children, who were aged between five and 14 at the time of the offences, were made to believe they were in severe pain.

They were given doses of opiates that in some instances were not prescribed for them.

In sentencing them, Judge Carmel Barbagallo described the offences as very serious, saying the administering of dangerous levels of the drugs to their daughter "had the potential to cause her death".

The mother, who was described by the judge as "the driving force" of the offending, was given a seven-year jail term while the father received four-and-a-half years.

The couple broke down crying in the dock as the sentences were handed down. 

Mother injected child from 'Alice in Wonderland bag'

The offences were uncovered when a medical professional raised the alarm after seeing the mother inject her daughter from a bag she referred to as the "Alice in Wonderland bag".

At the time, the children all used wheelchairs and were addicted to pain medication.

The court heard that since they had been taken into care, the three now had no use for wheelchairs, no longer complained of pain and were going to school and playing sports.

The woman's lawyer said his client also suffered from the same syndrome and she had projected her own experience with pain onto her children.

The father's lawyer said her client had largely left the day-to-day care of children in his wife's hands and he was unaware of the excessive doses she was giving them.

Children 'scarred for life'

As the couple's two sons watched proceedings via video link from another location, Judge Carmel Barbagallo said some of the medications were given to the children despite medical staff telling their mother to stop administering the drugs to them.

"Both of you knew, or should have known, the medications were unnecessary and not safe," Judge Barbagallo told the couple.

The court heard the three children had now been weaned off all medications, but they had suffered psychological and physical harm including years of opiate addiction and dependence on pain medication.

"To say the effects are significant and far reaching is an understatement," Judge Barbagallo told the couple.

"They had no idea what you were doing was wrong.

"You, their parents, have scarred your children for life."

The mother will have to serve five years before she can be released, while her husband will be eligible for parole after two-and-a-half years.