Alexandra Walker, 26, and Harrison Simpson, 22, have been sentenced to life imprisonment for the murder of two-year-old Isabelle Welsh.
The sentencing took place at Teesside Crown Court.
Simpson received a minimum term of 28 years and six months for murder, child cruelty, and sexual assault.
Walker was ordered to serve at least 22 years for murder and child cruelty.
The court heard that Isabelle suffered 21 broken bones in the weeks before her death at her home in Thornaby, Teesside.
Medical staff had raised concerns when Walker brought the toddler to a hospital with a broken leg, but the mother delayed further treatment.
When Isabelle collapsed, Walker hesitated before calling emergency services. CCTV showed her smoking a cigarette while searching online about the toddler's symptoms.
Paramedics found the child covered in bruises before she died in hospital the following day.
Court Proceedings
Prosecutor Richard Wright KC detailed the extent of the violence inflicted on the toddler.
"For weeks this child had been violently assaulted and her death, by that terrible head injury, was simply the end point in that campaign of violence to which she had been subjected," he said.
Ms Justice Norton addressed the defendants during sentencing, stating, "I have no doubt whatsoever that your lack of urgency or concern for your child was because you wrongly believed that Isabelle was already dead, and you were working out what to do to save your own skin."
She added, "Any death is a tragedy.
The death of a very young child at the hands of those who should have cared for, protected, and loved her – as she no doubt loved them – is particularly distressing for all involved."
Addressing Walker directly, the judge noted her persistent dishonesty: "Right to the very end, your interest was not in Isabelle, but in yourself."
DCI Chatterton of the investigating team said, "This has been, without a doubt, one of the worst cases my team and I have dealt with."
Isabelle's family issued a statement expressing their grief: "Isabelle should have had her whole life ahead of her, but she was taken from us in the most heartbreaking way."
They added, "She was so loved and our lives will never be the same without her.
While today's verdicts cannot undo the pain caused or bring Isabelle back, it does mean justice has been served."
The family concluded, "We will remember Isabelle forever."
