Brandy Niemiec, a 19-year-old Yonkers mother, was sentenced to five years' probation in a case in which prosecutors said she shook her 1-month-old son so violently he wound up with bleeding on the brain and a broken rib.

Niemiec pleaded guilty to second-degree assault in connection with the Aug. 23, 2012, incident at her family's Yonkers home. She was sentenced in Westchester County Court by Judge Lewis Adler. The judge also signed an order of protection forbidding Niemiec from having contact with the child until at least 2021.

A tearful Niemiec did not speak at her sentencing. But her Westchester Legal Aid Society lawyer Anne Bianchi said Niemiec was sorry about the incident.

Yonkers police said Niemiec confessed to harming the child.

"During this conduct the defendant stated she heard cracking come from the child's body," Yonkers Police Det. Dean Politopoulos said in a felony complaint filed against Niemiec.

The baby -- whose name was not released by authorities -- was born July 14.

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Niemiec shook the baby boy while putting him to sleep in his crib.

The baby's father -- who has custody of the boy -- was in court during the sentencing but did not speak to reporters later.

The baby is developing normally and has not shown any lingering effects from the incident, authorities said.

Officials said they won't know until the child is about 2 years old whether there will be any developmental damage as a result of what the young mother did to him.

Niemiec's court-appointed lawyer did not immediately return a call seeking comment.