Waiter Liam Whoriskey, 25, of Glenabbey Gardens in the city, denies murdering the toddler over two years ago.
The toddler was found dead in his family home at Colmcille Court in the Bogside on Sunday, September 17, 2017.
It is the prosecution case that Kayden sustained a series of blunt force trauma injuries to his and medical experts said they were “non-accidental” injuries. He was also found to have a broken rib.
The BBC reports that Toni Connor also told the jury that the defendant assaulted her several times during a three-year relationship.
In her evidence at Derry Crown Court, Ms Connor said her relationship with the defendant had begun in January 2012, when they were both aged 18.
Three months later, she became pregnant and their son was born in November 2012.
She told the court both she and the defendant lived with their respective parents.
Ms Connor said said the defendant would normally become aggressive when he had three or four drinks or more.
In July 2013, when both she and the defendant had been drinking, the witness said they had an argument during which the defendant pinned her to a wall and twisted her arms up her back, the court heard.
When she went out with friends, Ms Connor said, she never left her son alone with the defendant and normally got her sister or a friend to stay with her son and the defendant.
The court was told Ms Connor “never felt comfortable” leaving her son alone with the accused.She told the court that on another occasion when she had returned home after being out socialising and told the defendant that she had met another of his previous girlfriends in a bar and that she had been giving her “dirty looks”.
The defendant reacted by again pinning her to a wall and by throwing glasses about the room, she said.
She alleged that during some of their arguments the defendant shouted into their son’s face that “your mum’s a slag, she’s a rat”.
Ms Connor told the court the defendant swore at their son if he was making noise while he was watching television.
Under cross examination by defence counsel Ciaran Mallon QC, Ms Connor agreed that the defendant had never used violence towards their son.
Mr Mallon said social services had investigated the witness’s allegations.
“They concluded your allegations had no substance, they closed the file”, defence said.
Ms Connor agreed that she had not made a statement to the police about her allegations.
The defence barrister said the defendant would deny the witness’s allegations to which Ms Connor replied: “He’s lying”.
The witness also denied the assertion that she was “trying to spite Liam Whoriskey”.