Heartbreaking footage shows a toddler playing happily in the weeks before she was allegedly sexually assaulted and murdered by her mother and her new boyfriend.

Isabelle Welsh, two, suffered 21 broken bones in the weeks before she died from a serious head injury in September last year.

Her mother Alexandra Walker, 25, and Walker's boyfriend of just a few months, Harrison Simpson, 22, are accused of a 'campaign of violence' which ended in Isabelle being found fatally injured with 97 soft tissue injuries.

Walker and Simpson, who she had known for just a few months after meeting online, deny murder, assault by penetration, allowing the death of a child and child cruelty. 

Jurors at Teesside Crown Court were shown video footage of Isabelle playing at home before the weeks of alleged cruelty began.

In one clip she is charging around on the sofa at her mother's home in Thornaby, Teesside, leaping care-free from one side to the other.

And in another clip she runs up and down the small back garden clutching a red witch's hat to her head and laughing as it falls to the ground.

Within days of the second clip being filmed, Isabelle's life changed when she became the subject of prolonged abuse, injury and neglect from Simpson and Walker, the prosecution allege.

Teesside Crown Court has heard that in one incident Isabelle suffered a broken leg after being left alone with Simpson, but medical help was not sought for a fortnight while the toddler's pain worsened day after day.

She died in the early hours of September 14th last year after being found by paramedics lying motionless at the foot of the stairs.

She had suffered a catastrophic head injury which was consistent with being hit against a hard and unyielding surface such as a wall or the floor. The impact was so severe it stopped her heart.

The trial has heard Isabelle had suffered multiple broken bones and internal tears from violent sexual assaults, she had soft tissue injuries from fingertips where she had been tightly held and shaken and there was evidence from a pathologist to say she appeared to have been swung by a limb.

The court has heard that even as Isabelle lay dying, her mother waited just short of an hour before dialling 999.

She Googled 'Why would my toddler be bleeding?' as she walked around her kitchen smoking a cigarette, it is alleged.

It was only when her stepfather arrived at her home and insisted emergency services were called that she rang for help.

But Isabelle could not be saved despite the intervention of a team of doctors at North Tees Hospital.

Jurors were played an interview that maternal grandmother Claire Walker gave to detectives following Isabelle's death.

She told police the toddler was chatty and intelligent and had generally been in good health up to her sustaining a broken leg for which she received hospital treatment. Jurors have been told this was 11 days before she sustained a fatal head injury.

After the mother and toddler were allowed home from hospital, Isabelle's grandmother visited them and spotted a bruise on her back. She told detectives she said 'what the hell' when she saw it.

Ms Walker told police her daughter explained that Isabelle had bumped her head on the settee. She told police she thought Isabelle had picked up a virus from hospital which explained why she looked unwell.

The grandmother also gave evidence in court from behind a screen and told Mark McKone KC, representing her daughter, that she had never met Simpson, who had been dating Walker for just a few months. Ms Walker told the court her daughter explained that Simpson 'had anxiety and didn't want to meet with me'.

The trial, expected to last up to six weeks, continues.