Sara Ege, 31, a maths and statistics graduate, denies murdering her son and trying to pervert the course of justice by starting the fire, in a trial expected to last several weeks.
Her husband Yousef Ali Ege, 36, a city taxi driver who also works weekends in the Penarth Road Royal Mail sorting office, denies failing to take steps to protect his son.
Iman Yaquoub Kutkut, who taught Yaseen the Koran most weekdays at the Darl Isra mosque, said: “He was a cute boy, happy, confident, he always came on time.
Mr Kutkut said he had not seen Yaseen with any injuries or disabilities during the time he taught him.
Arabic teacher Amina Chabaan described Yaseen as an intelligent, hard working little boy during the time she gave him lessons.
Yaseen attended classes at the Channel View Centre most weekends from September 2009 onwards.
Mrs Chabaan said: “Yaseen was a lovely little boy, very intelligent, smart, very polite. He was very active in the class. Always smiling and seemed a very happy boy.”
As she spoke father Yousef Ali Edge wept in the dock, and mother Sara Edge bowed her head.
Mrs Chabaan said she noticed Yaseen had a problem with his leg that affected him when he moved.
She asked Sara Ege what had happened and was told Yaseen had had an operation.
Mrs Chabaan said she had no concerns about Mrs Ege’s parenting and Yaseen seemed happy, although he was a very quiet child.
She said: “When I used to see Sara with him, she had a very good way with him. I didn’t see him as at any risk.”
After the fire, Mrs Chabaan had visited Sara Ege and asked what had happened and was told an electrical fault had caused the blaze.
Karen O’Shea treated Sara Ege when she and her son were brought to University Hospital Wales at around 7.30pm on July 12 following the fire.
She said Sara Ege had not asked about what had happened to her son while she was been treated.
Mrs O’Shea said: “She didn’t ask at all. She didn’t ask anything about him at all. I found that very unusual.”
Sara Ege’s defence suggested she may not have asked as she already knew her son was dead.
Reading from Mrs O’Shea’s statement, he said she had described Yousef Ege arriving at the hospital.
He said: “(You said) the father arrived some time later. He marched straight up to Sara and said what happened, where were you?
“I found his manner very aggressive toward his wife. He seemed to blame her. I was worried about his tone and thought he might kick off. Sara was crying at this point.”
Mrs O’Shea agreed this had been the case.
Yousef Ege’s defence said he had not home to the cubicle where his wife was been treated, but Mrs O’Shea said he went there twice including when he told his wife their son was dead.
The trial continues.