A judge sentenced a Brooklyn father to 25 years to life behind bars Wednesday for the fatal beating of his 16-month-old daughter, after describing him as a “child” because he was only 18 when he committed the crime.

“This case is an unspeakable tragedy. A baby is dead at the hands of another child. He was 18 years old,” Brooklyn Supreme Court Justice Vincent Del Giudice said.

Nylah Lewis was killed after her mom, Tammy Lewis, dropped her off to spend Father’s Day with Shaquan Taylor in June 2017.

Tammy Lewis sobbed in the courtroom as prosecutor Frank DeGaetano read aloud a letter she wrote to the judge, saying the loss of her daughter meant she would never have children again.

“I don’t think I will ever want any more kids. I only wanted one kid,” Lewis wrote. “She was a happy baby.” She asked DelGiudice to lock Taylor away forever. “If he could do this to his only daughter, he could do it to anyone else,” she wrote.

Taylor declined to address DelGiudice, while his attorney, Jonathan Fink, asked the court to take the killer’s age into consideration.