Three children have begun testifying against their aunt and uncle, whom the Crown says beat and tortured them after adopting them into their Calgary home.

The children's parents were killed in a horrific car crash in the U.S., more than a decade ago. Police pulled the two girls and one boy, all under the age of 10, from the same fiery wreck. The orphaned children went to live with their maternal aunt and her husband after the crash, and were adopted by the Calgary couple in 2009.

"Unbeknownst to them or anyone in the family, a new ordeal began," Crown prosecutor William Tran said in his opening statement.

The three siblings began their testimony in a Calgary courtroom on Tuesday, where they started to delve into the allegations against their aunt and uncle. The charges against the couple include assault causing bodily harm and assault with the weapon.

"You will hear from all three of the children," the Crown told the court in its opening statement. "They will tell you how they were punished with punches, kicks and slaps to the head and body… how they were placed in cold showers, time and again."

The Crown says the alleged abuse came to light in 2011, when a teacher noticed the middle child had a swollen and bruised face. The Crown says the child was sent to speak to a school counsellor, to whom the child gave a "detailed recollection of a history of abuse."

The Crown alleges the oldest girl, now 19, had her tongue burned with a lighter. She appeared in court via CCTV on Tuesday and watched her original interview with police from 2011.

The judge has not yet ruled on whether what he heard from the oldest sister is admissible as evidence. The defence contends she made up the allegations and influenced her younger siblings.

All three children's identities are protected by a publication ban due to the age of the younger siblings.

None of the allegations have been proven in court.

With a report from CTV’s Alberta Bureau Chief Janet Dirks